Minecraft wiki entry for Development_versions, associated text: Biome placement is a bit smoother and less noisy. Fewer microbiomes dotting the terrain. Biomes tend to be a bit larger and less fragmented.
Underground biomes interfere less with surface biomes. They can still leak out of cave entrances sometimes.
Increased the height of some of the peaks.
Now can rarely reach up to Y=260.
Slightly increased the chance of finding large areas with flat terrain.
Structures now mostly show up in the right biomes.
Toned down the megacave entrances a little bit, and made them less likely to go all the way down to deepslate level.
Made cheese caves a little bit smaller on average, and a bit less likely to intersect the surface.
Reduced the chance of sand and gravel being placed in such a way that they immediately fall down on generation.
Some are now replaced with sandstone or stone.