I've seen a few world-type ideas, but I had one idea that I'd thought through a lot, and would also be quite possible with the existing in-game resources. So I submit for your approval my idea: The Wasteland.
Inspired by dystopian future-world adventure games like Fallout and STALKER, the Wasteland would be a new world type (without guns) that is bleak and, at first, appears barren. On spawning, the player is surrounded by a world of dirt and stone. No grass. The sun is small-looking and low on the horizon (the sky turns on a very shallow angle now), and the brightness is a mere twilight at high noon. Just light enough that dangerous mobs don't spawn, but only by a light level or two. The default terrain itself should generally be rounder and less random than a Normal world, but there should still be hills and such. General earth composition will be similar, a variable layer of dirt on top of a stone base dozens of blocks deep to bedrock. Mountains, Cliffs, Deserts, and Mushroom biomes will remain as is, including how rare the Mushroom biome is. Plant growth occurs according to normal rules, though the low light levels will make it difficult to see anything productive without the player helping out. Cows, sheep, and chickens are nearly impossible to find outside of certain locations (see below) though pigs may spawn, albeit less commonly. With the scarcer biology, hunger is a bigger enemy than ever. Players will find themselves hunting zombies for meat and chasing spiders to get string for bows and fishing rods more desperately. Basically green plantlife is nearly absent, and past signs of habitation everywhere but worn down or deteriorated. To give a better idea of what the world would be like, we can talk about its biomes and terrain features:
--== New Biomes ==--
--Shallow Sea
A vast body of water, like the Ocean biome, but shallower, no more than 2-4 blocks deep. Squid spawn in their normal retarded numbers. Fishing is still available, perhaps even a little easier, since the ocean's abundance is now compressed into less water.
--Stone Forest
Rolling, easy hills, but what makes this area unusual are tall stone spires frequently shooting up out of the dirt. These will be slightly more than single block pillars, anywhere from 1-4 blocks across at the base, but will easily reach 12-20 blocks in height. They are scattered as closely as trees in a regular forest. That's all, though.
--Broken Land
Broken lands are dangerous travel. The area is criss-crossed with mini-ravines about half the depth as regular versions but with the same length, and in some places chunks of the sundered earth have abruptly and roughly raised or lowered themselves. The mini-ravines are about half the depth of regular ones, but their quantity could make it easy to misstep. On the other hand, with the many raised and lowered sections of earth exposed, open-to-surface mining prospects could be lucrative...
--Saltflats
Large expanses of sand, similar to deserts, but with many shallow, wide ponds and near-complete flatness. Clay is abundant here, in and out of the water, and low, small, clay humps 5-7 blocks across and 3-4 blocks high dot the landscape. No plants, too salty.
--Gravel Plains
Plains. Of gravel. There are exposed patches of cobbles in some places, too. The plains are crossed with swathes of brown tall grass, large clusters of dead shrubs and possibly patches of mycelium. Mushrooms growing on mycelium will be of the short variety only.
--Scrubland
Scrublands are generally brown, brown, and more brown, and are scattered with barely-surviving grasses. They are also regularly dotted with stunted shrub-trees only a couple blocks high (like jungle underbrush, but instead of in ground-covering clusters, these shrub-trees stand singly. There are random stone blocks in the rocky soil, and small, gravel-bottomed pools. But at least there's a few harvestable logs here from the shrub-trees. They are only 1 or 2 logs tall, but its better than nothing.
--== Terrain Features ==--
--Crater
You'll know a Crater when you encounter a curving low wall of dirt that is rather wide. The wall will be about 2-5 blocks high, with a slope up the side. When you reach the top of the wall, however, you will find a vast gaping hole anywhere from 25-60 blocks across. Also, the Crater has a rather variable depth. It will usually be somewhere around 7-12 blocks deep, but it could go much deeper, say 20 or even 30 blocks down, though these depths will be pretty rare. The bottom center of the Crater may or may not have a lake in it, and the lowest couple of layers will be lined with abundant coal, (because charcoal doesn't have a block), patches of gravel, and a few random blocks of obsidian closer to the center. There is a common possibility that a small peak a few blocks tall may have formed in the center, and this may be stone, dirt, gravel, or, rarely, obsidian. Deep Craters will expose lots of underground caves and formations, and perhaps lucky finds of ore and minerals, but if the Crater is deep, the inner slope could be quite dangerous to navigate because of the risk of falling. Also, any lava the crater exposes may flow into the Crater and spread as well.
--Hidden Valley
Hidden valleys are pretty rare (about as common as normal dungeons), and will typically appear in hilly areas, and can be in abruptly deep holes in the ground, a dozen or so blocks deep. They are walled with dirt and stone, and feature a few trees and patches of grass at the bottom. Valleys may actually sport some other plants as well, like tall grass, vines, and on rare, rare occasions a flower or two. A valley may have a spring or two in its walls or sport a pond with lily pads in it and maybe some sugar cane. Passive mobs may spawn here as normal.
--Dead City
Ruined buildings in a large area, about twice the size of a Normal NPC Village. The buildings are just squares or rectangles with some window and occasionly, stone or step roofs. They have no doors or glass, and sometimes whole walls or corners are missing. Sometimes one can find blocks of wood in some corners of the empty buildings, or even an entire upper floor of wood planks. There may be one or two two-story buildings, but they are generally squares with nothing more than a stone stair case. Buildings can be stone, brick, or stone brick. There could also be just flat walls here and there, not part of any buildings. Damaged walls in buildings or standing alone are edged with cobble, and some buildings will have cobble piles in them. Cobble piles may have a chest spawned underneath them, with some iron, perhaps a tool or some raw materials, generally nothing organic other than an occasional seed. More often than not, though, it will be just a block or two of wood planks, or more cobble. Dead Cities can be somewhat dangerous, as mobs are generated in this area, and also can spawn inside many of the darkened, roofed buildings (any torches have burned out ages ago). Also, skeletons and zombies are spawned frequently here, remnants of a lost society. You can have those easy buildings, if you can defend them from lost spirits of the past...
--Tunnels
Man-made halls boring through the ground, these are lined with stone brick on the walls and ceiling, and often slope up or down or make wide turns. The floor of a tunnel is gravel or cobble, and torches may have been left behind to light certain parts. They will be about 1.5x the size of nether fortress tunnels, for comparison. The Tunnels often have cobble, gravel, and stone cave-ins coming from the walls or ceiling, and every now and then may have a small side utility room with a lever-operated iron door that could have a chest with metals, tools, lumber, etc in it. Tunnels only rarely branch and can continue on for some distance, occassionally breaking up to the surface, and can appear at any elevation, but only spawn in-ground. (no 'sky-tunnels')
--Sub-Terra Village
Lurking omniously in large, dome-shaped caverns, there exist small tribes who escaped the surface's barrens to the safety of the underground. These will be almost exactly like normal villages, perhaps a little smaller, but about 150% more densely populated. Houses will be generated more closely together in a ring around a well (still at least a block apart from each other, though), with perhaps a couple or three outlying homes. A 2-3 block wide gravel path will ring the well. Many of these homes will be partially embedded in the surrounding rock if the cave is not that big. There will be 1-3 farm-caves linked with the main village, wheat farms being most common, but there is a chance of the farms containing a fenced area with 2-4 cows, sheep, pigs, or chickens. Farms are very well torch-lit. Golems could spawn under normal rules, but will be very unlikely since sub-terra villages are spawned smaller. It'd take player intervention to generate a golem. It is also possilbe to generate these villages at any ground level, meaning they could be on the surface. They could also be inundated with lava or water, though... poor villagers...
--Minor Terrain Features
-Short lengths of tracks on the surface. These can appear anywhere there is exposed surface blocks, in any biome. Uncommon.
-Dead trees. Smallish branched trees, but with no leaves. Get yer logs and move on, Steve...
-Lost farm. One lonely house, possibly damaged walls, no glass. May or may not have a wood-floored attic with common materials in a chest. May also have a fenced in area, but nothing in it.
-Ravines can occasionally have a bridge somewhere on their highest point, either wood or cobble with cobble or wood fence railings. If this happens on an underground ravine, well... I suppose it used to be on the surface...
--Facility (stronghold replacement)
Instead of strongholds, there are facilities. They will be similar to strongholds, in that they are lined with stonebrick, have iron doors with buttons, and are extensively large. They will also have the requisite Endgate, of course. The special rooms are more abundant, but only because there are more types. They are still infrequent.
-----------
-Many long hallways with rooms on either side instead of randomly connected rooms. Most of these rooms will be boring and empty.
-Plenty of the usual staircases, spiral stairs, dead ends, etc.
-Silverfish are not normally found in facilities, but may appear in special rooms.
-Instead of torches, there are redstone lamps with levers in rooms and at the ends of hallways. These will spawn unactivated, and the facility will be very dark, forcing the player to find the light switches and deal with whatever the darkness spawns. Or at least they should bring lots of torches.
--== Room types ==--
---Barracks: Long, wide rectangular rooms with beds in two neat rows, and a chest at the foot of each bed. The chests will typically be empty, but may rarely contain common materials, but every barracks will have 7-10 skeletons or zombies (one type or the other) locked inside behind the barracks door. This could suck if the room is breached somehow before the player arrives and the skellys can just come streaming out right away. These will spawn in limited quantity, no more than 2-3 max per facility.
---Chem Lab: A medium small room with double-slab block counters around the walls and a couple rows of slabs in the middle. A few brewing stands will be here and there on the counters, a bookcase or two, and maybe a chest with bottles or possibly a random potion in it.
---Bio Lab: Similar to a chem lab without the chest, the bio lab is enlarged by 2-3 adjacent containment cells with iron bar front walls which may contain a random aggressive mob (or zombie pigman). If silverfish is selected to be in a cell, several are spawned to infest the cell's wall blocks, potentially releasing other monsters from the other cells. A cell may also contain a squished-in tree. Science!
---Forge: A room with one or more rows of furnaces at eye level in the walls, and and a trough of lava 3-5 blocks long.
---Experiment room: Spawns as a regular dungeon, but no chests, and the walls are stonebrick or slimy stonebrick. Spawner may equally be skeleton, spider, zombie, blazer, silverfish, or cave spider. No doors. Oh, snap.
---Containment Cellblock: Like a regular hallway, but instead of stone walls with doors, this hall will have iron bar walls with doors. Stonebrick pillars will be at the corners of each cell for both appearances and to provide a button block for the cell doors. Cells may or may not have beds or a slab in them. If there is a lamp, it will only be at the entrance to the cell block. If the hall is a dead end, there may be a water pool at the end. This area may be positively loaded with silverfish in addition to normally spawned creatures, beware!
---Offices: small square rooms with a wood stairs block 'chair' in front of a double slab 'desk'
---Mess hall: a randomly sized room with rows of fence/wood floorplate tables. A slab counter lines one wall, and will have a chest behind it that might have food in it.
---Checkpoint: Just two iron gateways in a row with iron doors activated by floorplates.
Ok, so, biomes are a huge pain to build, so here's a couple of features. I am working on examples of Facility rooms, dead city, and small patches of the biomes. I'm not doing a crater or a shallow sea. You'll just have to imagine those. But more will be coming, if people are interested.
-=-=-=-=-=-=-
Sub-Terra Village. I put villagers in there, but for some reason, they all piled into one house. Wierd.
Another shot of the village, showing the chicken farm. Pay no attention the patch of grass I forgot to clear out.
A Tunnel entrance, with utility room.
And another shot of the tunnel, showing its scary-ness.
Inspired by dystopian future-world adventure games like Fallout and STALKER, the Wasteland would be a new world type (without guns) that is bleak and, at first, appears barren. On spawning, the player is surrounded by a world of dirt and stone. No grass. The sun is small-looking and low on the horizon (the sky turns on a very shallow angle now), and the brightness is a mere twilight at high noon. Just light enough that dangerous mobs don't spawn, but only by a light level or two. The default terrain itself should generally be rounder and less random than a Normal world, but there should still be hills and such. General earth composition will be similar, a variable layer of dirt on top of a stone base dozens of blocks deep to bedrock. Mountains, Cliffs, Deserts, and Mushroom biomes will remain as is, including how rare the Mushroom biome is. Plant growth occurs according to normal rules, though the low light levels will make it difficult to see anything productive without the player helping out. Cows, sheep, and chickens are nearly impossible to find outside of certain locations (see below) though pigs may spawn, albeit less commonly. With the scarcer biology, hunger is a bigger enemy than ever. Players will find themselves hunting zombies for meat and chasing spiders to get string for bows and fishing rods more desperately. Basically green plantlife is nearly absent, and past signs of habitation everywhere but worn down or deteriorated. To give a better idea of what the world would be like, we can talk about its biomes and terrain features:
--== New Biomes ==--
--Shallow Sea
A vast body of water, like the Ocean biome, but shallower, no more than 2-4 blocks deep. Squid spawn in their normal retarded numbers. Fishing is still available, perhaps even a little easier, since the ocean's abundance is now compressed into less water.
--Stone Forest
Rolling, easy hills, but what makes this area unusual are tall stone spires frequently shooting up out of the dirt. These will be slightly more than single block pillars, anywhere from 1-4 blocks across at the base, but will easily reach 12-20 blocks in height. They are scattered as closely as trees in a regular forest. That's all, though.
--Broken Land
Broken lands are dangerous travel. The area is criss-crossed with mini-ravines about half the depth as regular versions but with the same length, and in some places chunks of the sundered earth have abruptly and roughly raised or lowered themselves. The mini-ravines are about half the depth of regular ones, but their quantity could make it easy to misstep. On the other hand, with the many raised and lowered sections of earth exposed, open-to-surface mining prospects could be lucrative...
--Saltflats
Large expanses of sand, similar to deserts, but with many shallow, wide ponds and near-complete flatness. Clay is abundant here, in and out of the water, and low, small, clay humps 5-7 blocks across and 3-4 blocks high dot the landscape. No plants, too salty.
--Gravel Plains
Plains. Of gravel. There are exposed patches of cobbles in some places, too. The plains are crossed with swathes of brown tall grass, large clusters of dead shrubs and possibly patches of mycelium. Mushrooms growing on mycelium will be of the short variety only.
--Scrubland
Scrublands are generally brown, brown, and more brown, and are scattered with barely-surviving grasses. They are also regularly dotted with stunted shrub-trees only a couple blocks high (like jungle underbrush, but instead of in ground-covering clusters, these shrub-trees stand singly. There are random stone blocks in the rocky soil, and small, gravel-bottomed pools. But at least there's a few harvestable logs here from the shrub-trees. They are only 1 or 2 logs tall, but its better than nothing.
--== Terrain Features ==--
--Crater
You'll know a Crater when you encounter a curving low wall of dirt that is rather wide. The wall will be about 2-5 blocks high, with a slope up the side. When you reach the top of the wall, however, you will find a vast gaping hole anywhere from 25-60 blocks across. Also, the Crater has a rather variable depth. It will usually be somewhere around 7-12 blocks deep, but it could go much deeper, say 20 or even 30 blocks down, though these depths will be pretty rare. The bottom center of the Crater may or may not have a lake in it, and the lowest couple of layers will be lined with abundant coal, (because charcoal doesn't have a block), patches of gravel, and a few random blocks of obsidian closer to the center. There is a common possibility that a small peak a few blocks tall may have formed in the center, and this may be stone, dirt, gravel, or, rarely, obsidian. Deep Craters will expose lots of underground caves and formations, and perhaps lucky finds of ore and minerals, but if the Crater is deep, the inner slope could be quite dangerous to navigate because of the risk of falling. Also, any lava the crater exposes may flow into the Crater and spread as well.
--Hidden Valley
Hidden valleys are pretty rare (about as common as normal dungeons), and will typically appear in hilly areas, and can be in abruptly deep holes in the ground, a dozen or so blocks deep. They are walled with dirt and stone, and feature a few trees and patches of grass at the bottom. Valleys may actually sport some other plants as well, like tall grass, vines, and on rare, rare occasions a flower or two. A valley may have a spring or two in its walls or sport a pond with lily pads in it and maybe some sugar cane. Passive mobs may spawn here as normal.
--Dead City
Ruined buildings in a large area, about twice the size of a Normal NPC Village. The buildings are just squares or rectangles with some window and occasionly, stone or step roofs. They have no doors or glass, and sometimes whole walls or corners are missing. Sometimes one can find blocks of wood in some corners of the empty buildings, or even an entire upper floor of wood planks. There may be one or two two-story buildings, but they are generally squares with nothing more than a stone stair case. Buildings can be stone, brick, or stone brick. There could also be just flat walls here and there, not part of any buildings. Damaged walls in buildings or standing alone are edged with cobble, and some buildings will have cobble piles in them. Cobble piles may have a chest spawned underneath them, with some iron, perhaps a tool or some raw materials, generally nothing organic other than an occasional seed. More often than not, though, it will be just a block or two of wood planks, or more cobble. Dead Cities can be somewhat dangerous, as mobs are generated in this area, and also can spawn inside many of the darkened, roofed buildings (any torches have burned out ages ago). Also, skeletons and zombies are spawned frequently here, remnants of a lost society. You can have those easy buildings, if you can defend them from lost spirits of the past...
--Tunnels
Man-made halls boring through the ground, these are lined with stone brick on the walls and ceiling, and often slope up or down or make wide turns. The floor of a tunnel is gravel or cobble, and torches may have been left behind to light certain parts. They will be about 1.5x the size of nether fortress tunnels, for comparison. The Tunnels often have cobble, gravel, and stone cave-ins coming from the walls or ceiling, and every now and then may have a small side utility room with a lever-operated iron door that could have a chest with metals, tools, lumber, etc in it. Tunnels only rarely branch and can continue on for some distance, occassionally breaking up to the surface, and can appear at any elevation, but only spawn in-ground. (no 'sky-tunnels')
--Sub-Terra Village
Lurking omniously in large, dome-shaped caverns, there exist small tribes who escaped the surface's barrens to the safety of the underground. These will be almost exactly like normal villages, perhaps a little smaller, but about 150% more densely populated. Houses will be generated more closely together in a ring around a well (still at least a block apart from each other, though), with perhaps a couple or three outlying homes. A 2-3 block wide gravel path will ring the well. Many of these homes will be partially embedded in the surrounding rock if the cave is not that big. There will be 1-3 farm-caves linked with the main village, wheat farms being most common, but there is a chance of the farms containing a fenced area with 2-4 cows, sheep, pigs, or chickens. Farms are very well torch-lit. Golems could spawn under normal rules, but will be very unlikely since sub-terra villages are spawned smaller. It'd take player intervention to generate a golem. It is also possilbe to generate these villages at any ground level, meaning they could be on the surface. They could also be inundated with lava or water, though... poor villagers...
--Minor Terrain Features
-Short lengths of tracks on the surface. These can appear anywhere there is exposed surface blocks, in any biome. Uncommon.
-Dead trees. Smallish branched trees, but with no leaves. Get yer logs and move on, Steve...
-Lost farm. One lonely house, possibly damaged walls, no glass. May or may not have a wood-floored attic with common materials in a chest. May also have a fenced in area, but nothing in it.
-Ravines can occasionally have a bridge somewhere on their highest point, either wood or cobble with cobble or wood fence railings. If this happens on an underground ravine, well... I suppose it used to be on the surface...
--Facility (stronghold replacement)
Instead of strongholds, there are facilities. They will be similar to strongholds, in that they are lined with stonebrick, have iron doors with buttons, and are extensively large. They will also have the requisite Endgate, of course. The special rooms are more abundant, but only because there are more types. They are still infrequent.
-----------
-Many long hallways with rooms on either side instead of randomly connected rooms. Most of these rooms will be boring and empty.
-Plenty of the usual staircases, spiral stairs, dead ends, etc.
-Silverfish are not normally found in facilities, but may appear in special rooms.
-Instead of torches, there are redstone lamps with levers in rooms and at the ends of hallways. These will spawn unactivated, and the facility will be very dark, forcing the player to find the light switches and deal with whatever the darkness spawns. Or at least they should bring lots of torches.
--== Room types ==--
---Barracks: Long, wide rectangular rooms with beds in two neat rows, and a chest at the foot of each bed. The chests will typically be empty, but may rarely contain common materials, but every barracks will have 7-10 skeletons or zombies (one type or the other) locked inside behind the barracks door. This could suck if the room is breached somehow before the player arrives and the skellys can just come streaming out right away. These will spawn in limited quantity, no more than 2-3 max per facility.
---Chem Lab: A medium small room with double-slab block counters around the walls and a couple rows of slabs in the middle. A few brewing stands will be here and there on the counters, a bookcase or two, and maybe a chest with bottles or possibly a random potion in it.
---Bio Lab: Similar to a chem lab without the chest, the bio lab is enlarged by 2-3 adjacent containment cells with iron bar front walls which may contain a random aggressive mob (or zombie pigman). If silverfish is selected to be in a cell, several are spawned to infest the cell's wall blocks, potentially releasing other monsters from the other cells. A cell may also contain a squished-in tree. Science!
---Forge: A room with one or more rows of furnaces at eye level in the walls, and and a trough of lava 3-5 blocks long.
---Experiment room: Spawns as a regular dungeon, but no chests, and the walls are stonebrick or slimy stonebrick. Spawner may equally be skeleton, spider, zombie, blazer, silverfish, or cave spider. No doors. Oh, snap.
---Containment Cellblock: Like a regular hallway, but instead of stone walls with doors, this hall will have iron bar walls with doors. Stonebrick pillars will be at the corners of each cell for both appearances and to provide a button block for the cell doors. Cells may or may not have beds or a slab in them. If there is a lamp, it will only be at the entrance to the cell block. If the hall is a dead end, there may be a water pool at the end. This area may be positively loaded with silverfish in addition to normally spawned creatures, beware!
---Offices: small square rooms with a wood stairs block 'chair' in front of a double slab 'desk'
---Mess hall: a randomly sized room with rows of fence/wood floorplate tables. A slab counter lines one wall, and will have a chest behind it that might have food in it.
---Checkpoint: Just two iron gateways in a row with iron doors activated by floorplates.
Pictures? Gah... well, er...um... I suppose I could go creative mode and come up with something. I'll be back...
-=-=-=-=-=-=-
Sub-Terra Village. I put villagers in there, but for some reason, they all piled into one house. Wierd.
Another shot of the village, showing the chicken farm. Pay no attention the patch of grass I forgot to clear out.
A Tunnel entrance, with utility room.
And another shot of the tunnel, showing its scary-ness.