Flawed as all hell.
As far as games of this kind go, it's been done better elsewhere. Take a look at "Dude and Zombies" for example. More or less the same concept, but done infinitely better.
The game lagged a fair bit and the method used to clearout the screen was a major annoyance. It's ridiculous that the player gets punished for killing enemies, when the money that should be a reward for killing the enemy is sucked away, as if to say "ha ha, fuck you" to the person playing the game. As someone else said, why not just have the debris fade away?
The other major issue is that you have to rely on an unbelievably slow healing process. Why is there no way of healing available to purchase in the store? Why not include health bonuses if somehow, allowing people to purchase their health back is an offensive concept to you for some reason? Shouldn't that sort of thing be standard?