One thing that has bugged me to no end is the fact that there are several animal spawn points under water.... It does not make sense, its easy to fix and it ruins the game when 1 type of animal only spawns (with the current server settings) under water.
Another thing is that all animal types have a fixed spawn location, no matter what server your on, there is 2 pigs in the north west near the tip, a wolf beyond it and 2 sheep (or rather 2 rams) just before it. (depending ofc on how many animals are in the game)
And if the animal count of the game is low enough, some animal types will not get spawned altogether.
Randomize the spawns more across the map, add spawn points, and let it randomly pick where animals will spawn, and let the type of animal spawned be random as well.
And if animals could roam some more, instead of moving left and right only about 10 blocks, free range animals roaming the lands would be a huge improvement.