Certainly good for a bout of mental gymnastics, though I wish the mechanics were a bit more inspired. I'd like to see more than just the simple shooting and adding up of numbers... maybe have alternate levels and characters that work on multiplication, exponents, etc.

I also lament that the game lags at times, so I might not hit the right target at the right time, and there doesn't appear to be any way of undoing your shot, and this has cost me more than a few lives.