I am sort of in the middle here, on one hand, I love Beta terrain probably the most. Maybe that is nostalgia, but I loved the sheer variety of terrain you got- massive cliffs, those enormous overhangs and I sort of miss the random "sandpits" you would find. That said I don't dislike the new generation, it just isn't quite so exciting, even with many more biomes. I also miss the continents you used to get, the world is currently like a Pangea and the oceans are in reality lakes, I sort of liked the adventure in crossing enormous oceans to new lands back in the early releases. One thing that could be improved upon in modern Minecraft is you can spawn in a world that due to the temperature of biomes is almost exclusively desert and savanna biomes. I am lucky in my world it is mostly the biomes I like most near spawn but that is pure luck.
Me too, I miss the adventurous aspect of it, it feels like most of everything is just mountains which get incredibly annoying and oceans don't seem to actually exist anymore. More so large rivers. I've found one seed out of about 4 I made that made me happy, everything else was very ugly and those stone mountains were an eyesore to say the least.