I like this, but you really could improve the whole thing by like 3 whole stars, just by adding some better graphics and soundeffects! As said, gameplay is perfect, and with graphics, this would be, in my opinion, a good game. Although maybe a bit variations like harder stages and such could be an increase aswell. But you will win much by just touching up the graphics.
It's sort of like a more dynamic version of Bust a Move. Being partial to that series, I can't help but like it, though. I think you have a good idea going here and it just needs a little tweaking with the physics, more colorfulness, and other things to make it more attractive. The amount of time for the stage was pretty long, I gotta say, but I suppose that was your intention seeing as this is probably a pilot flash. I'm guessing you might have different arrangements of floors or maybe more frequency of balls or maybe higher velocity or accelerating balls or even balls that give you bonuses or cause explosions or cause penalties of some form. Maybe adding a specific theme with each stage as the game progresses. Anyway, sorry for the long review.
Not a bad idea.
Maybe some music and a proper crosshair. Also, it's a bit hard at times, but that might be my suck-ass skills :)