We already told you that 14-year-old Robert Nay's free Bubble Ball is more popular than Angry Birds on iTunes right now. Let's see how the game runs and let's laugh together when it stumps me.
One of the lessons I've drawn from playing Bubble Ball is that if someone ever asks you to make a hit game, you should make a game that lets the players think about what they want to do, then do it, then get to watch how things unfold. Space those three things out and it should help. See: Angry Birds, Peggle, and Bubble Ball.
Fun game. No reason not to get it for your iPhone and iPad if you have one, since it's free. Unless you hate physics and the hard work of children.
Bubble Ball on iTunes (free)