Changes compared to experimental snapshot 1

Biome placement is a bit smoother and less noisy. Fewer microbiomes dotting the terrain. Biomes tend to be a bit larger and less fragmented.
Raised cloud level from 128 to 192.
Renamed mountains (= old mountains biome) to extreme hills, and gravelly mountains to gravelly hills, to reduce risk of people getting confused when they use /locatebiome to find the new mountains and end up in the old mountains...
Beachier beaches! Beaches are generally wider. But also in some places there are no beaches at all, to provide some variation.
Sheep spawn in meadows. Also more rabbits and less donkeys.
Blue orchid no longer spawns in meadows. The swamps were sad because this was their unique thing.
Swamps now generate properly. They generated in weird places before and were sad about that. Swamps are happier now.
Added missing biomes: Ice spikes and Eroded badlands.
Underground biomes interfere less with surface biomes. They can still leak out of cave entrances sometimes though (because it looks kinda cool!)
Increased the height of some of the peaks. Now they can reach up to 220-260 or so, but rarely.
Slightly increased the chance of finding large areas with flat terrain.
Meadows sometimes spawn a lone tree, often with a bee nest.
Monsters spawn in the new mountain biomes.
Emeralds and infested stone generate in the new mountain biomes
Made ore veins slightly larger and more frequent, since very few people seemed to actually find them in survival.
Structures now show up in the right biomes (mostly...). Found the right amount of duct tape to put in the right place in the code.
Toned down the megacave entrances a little bit, and made them less likely to go all the way down to deepslate level. Getting to diamond zone was just a bit too easy.
Made cheese caves a little bit smaller on average (they can still be huge though!), 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. Replaced with sandstone or stone in those cases. The falling blocks were messing up the terrain as well as performance. Still happens but not as as often.
Made Lush caves a bit smaller and a bit less common.
Zombie, Skeleton, spider and cave-spider spawners now spawn mobs up to block-light level 11. Although the mobs spawning in complete darkness did not affect the difficulty of vanilla spawners, we recognized that these spawners haven't been a real challenge for a while now. We hope this change will make conquering a spawner a more exciting challenge!
Spawners have a new "CustomSpawnRules" tag, which lets you override the spawn rules of the spawned mob. In the tag you can specify "BlockLightLimit" which indicates the highest block-light the spawners will spawn mobs at. This change is to enable map-makers to use spawners in a more customizable manner to spawn mobs in any light levels they choose!