really nice idea but i had some gripes.
didn't like the color choice at all.
having to do levels faster to unlock other levels was a bad design decision. this just isn't that type of game. at least it shouldn't be.
why levels? why not have it be one continuous world? do you have any idea how much that changes the overall feel?
obviously it needs some ambient noise. i agree with no music. but ambient noise would be great.
needs sound effects for collision between the ball and walls and other environmental things.
the core mechanic was great and the forces and inertias/accelerations felt just right. tuning that stuff is not trivial so you've got that going for you.
the art for the UI stuff looks very... old-school-flash'ish
i'd pixelate it or something.