1. The heat/humidity. Yes, I understand it. But that doesn't make me like it.
2. I agree that more ways to get from one place to another would be nice. I'd love paths from the Oasis to Dinoland or Pandora, for instance, instead of having to walk up to Discovery Island before branching off. It's not a major difference, but it seems silly to be on the same side of the river as those two lands, cross the river away from them, then cross it again to get back to first one, and back and forth again to the other.
3. Dinoland. It's just my least favorite area. The carnival thing just isn't what I'm looking for at WDW and while I like Finding Nemo, it just bugs me that they stuck it in Dinoland. You might as well just hang a sign that says "We couldn't be bothered to come up with a truly immersive Dinosaur area, so we threw in a dino-themed carnival and there was still more space, so what the heck, toss Nemo over there, too."
(The Dinosaur ride & boneyard are fine in my personal opinion.) I feel like they can either do better with Dinoland or they can just do something else there entirely.
That's it. Otherwise I really like Animal Kingdom.