In the new snapshots, each nether biome has different abundances of different mobs. This seems to have been taken too far, as the warped forest has so many endermen as to rival the end, and in the soul sand valley, ghasts spawn in and attack you faster than you can kill them off. Obviously, the mob spawning in the nether needs some work, especially regarding endermen. (Shouldn't they have the same abundance everywhere, as they do in the overworld?)