Well designed fun action game, I like others though wish the blood splatters were either fewer or a different color than hordes of zombies. Makes things irritating when you have a lot of zombies on the screen all at once.
Good challenging game, I never had the control problem other people are complaining about. Very good concept and coding, collision is done well as said by others.
As others have said, the ugprades make very very small diferences...mine system is cumbersome especially if you have a lot of them. Could be done better.
Game is well done and entertaining, while I will agree it is a guessing game somewhat if you really sit down and look at the puzzle before shooting it can be quite fulfilling.
Controls are a little sketchy on this, and the magic spells system is a little clunky in my opinion. I've also done the coin collector a couple times and not recieved the badge.
As others have said, once you have the minigun in survival it becomes quite trivial. The blood splatters left over on the floor after killing creeps becomes irritating and can help hide other creeps coming into the field.