The concept is good, but the game is simply too difficult once you get past the first boss. The robots spawn far too low down on the screen for it to be possible for you to stop them, since there's a cooldown of some description, plus the electric bar combined with the second boss' gimmick means your money is virtually cut down by three-quarters when you eventually reach the third boss. If the cooldown was reduced amogst other things, I think it'd be easier.