Only thing I could suggest would be some kind of skill tree (gemcraft style). The rest of the game is just perfect.
(Finished 5 levels and in this time the rating went up from 4.27 to 4.29 :)) )
@ crypto1337 : lvl 14 is easy. Just use your brain.
@ Delyius : Just count the count of balls that went off the screen. Would you like to click a button that might be far from the first piece you need to hover over :P?
It would be a pity if this game would not get some more levels in the same manner I saw here. Well built, difficulty curve right on the spot. And I love the fact that in some levels you can have other options of completing them. Keep up the good work.
Not bad for a first beta. The basic suggestions would apply. Try some score, purpose (target score in set amount of time), bigger points for center hits and some differences between weapons. All that presented in a short intro.