Not bad
Yes the concept is slightly overused, but I think you made up for that with the powerups. I certainly was not expecting a shooter powerup for a bomb placing game.
I think your game screen in relation to the size of the balls was far too small. The space to move around was hardly enough, combined with the rate at which the balls appear from the side of the screen. This also makes it hard to maneuver for those who want to go for the big kill - that being trying to lure as many balls together as possible before laying a bomb.
The swirly colour changing background was a nice touch, and sometimes the death of the player. Just when you thought it was safe to bump through the green ball to get out of a tight spot, the background changes and you die. It's a nice addition, but some players may find that annoying. I found it interesting and it added a new aspect of difficulty and challenge to the game. You might want to consider adding time intervals for each colour change for the player to see. I suppose it might make things easier, but with other things to concentrate on like moving around and placing bombs, I don't think it will make that much of a difference. And it'll prevent accidental deaths by bumping.
Oh, and let me return to the space issue. With so little space to move around it makes the shooter powerup relatively redundant. There's barely enough space to turn and shoot those pesky balls that are creeping nearer and nearer.
My suggestion is to make the playing field larger, and as the levels increase, make the balls faster. I think this would add a much more interesting challenege to the game. And the mouse sensitivity issue as mentioned earlier - faster response = allowance for faster moving balls.
Old concept, new twists. Nice touches, but a little more retouching could do this alot of good.