First of all congratulations on your second finished game, cause i haven't finished anything yet
I'm pretty tired now, so maybe that's a reason, but i find the platforms and caves in your game pretty annoying. You have to keep smashing the jump button to advance on almost every single square. I think you must take a little more time working on level design, and make some challenges. Maybe puzzles which need the bird to be solved, this kind of stuff. If you wanna keep on the actual gameplay, just work a little bit more on that platforms
The graphic desing was beautiful, with that birds of different colors and stuff, i liked it. But the caves (again) were repeating as hell.
Well, i hope i'd been of help. Keep on the good work and good luck with your games ^^
PS: Sorry about my english, as i said i'm pretty tired now. I hope i made my point.