I played the first 6 levels. The only frustrating thing is that this game seems to be designed for 2 players. It's hard to control both birds at once. Also, I think that both birds are required to be on screen at the same time, that should be explained. One of the levels (the one with two "floors" with one bird on each floor, and they have to both move to the right) is frustrating until I figured out that constraint.
To make it more attractive, pick a certain aesthetic and stick to it. It looks realistic but the rigid pattern of blocks all stacked neatly on top of each other to form the walls looks unrealistic. Make it more cartoonish and I think it would be better.