That was pretty good
But could you tweak the collision detection a bit? Sometimes it feels like you need to be really accurate to hit those blocks dead on and make them disappear. That or kind of make it so the cursor on the top of the screen can only move within the set rows, that would make it easier to shoot and then you wouldn't have to worry about the collision detection. Also, it seemed like sometimes blocks weren't disappearing correctly even when I hit them with an appropriate color.
I can recall one instance in which a black block was threatening to reach the top of the screen. I kept hitting it with whites, but it wouldn't disappear until a red showed up.
Anyway, other than that, it was a pretty decent game. Give it a little ironing out and you've got a real gem. Keep up the good work!!!