Two things kinda irking me with the Animation Editor:
First thing is, that I kinda wished you could choose around what point something rotates. From what I saw, you could only rotate a bone around the middle of it. In many cases, though, it'd be much easier to rotate them around the point where they actually connect to something.
The other thing, which I already mentioned in the chat, is that quitting the Animation Editor will bring you back to the title screen, instead of your mod. Maybe I'm just closing it the wrong way, but it would be better if it would automatically start the mod you came from again.