Its funny, I almost made this kind of game. I used to play this game with pen and paper when I was kid. I loved it, you gave justice to this classic game. Different levels make game very interesting. You shold unlock each level only after completing the current level rather than just letting user to select level. Best of luck.
BallsBreaker is a free game that runs in your iPhone and iPod. Lets Break some Balls! BallsBreaker