I think a great modded addition to Minecraft, with aggressive mobs being added through other mods, would be guns that would work like Doom/Quake. Instead of durability, the guns "durability" bar would show how much ammo is left for that weapon, which could be either added to the weapon through a crafting table, or work like Bows and Arrows. It would also be AMAZING if they could be 3d models instead of just sprites. They don't need to be centered on the screen, whatever is easier, but it would be a nice addition. Here's a mock-up I made, that will hopefully help you get what I mean, and maybe even spark interest for a mod with this in it.
If you want that gun model, it was made in Techne and I could give it to you if you want to make this mod. It only has the barrels though, no stock.