First of all, it's spelled cancel. Also, I feel like the revolver is under-powered, and the shotgun thing doesn't seem to do any damage at all. The hit detection is pretty sensitive, and headshots don't do any damage.I would also consider switching out the lead pipe with a crowbar for a more Half-Life feel instead of CS.
Slow at times, will even freeze up between waves. I'm not sure if that's what's causing enemies to spawn on-screen of if that's how you programmed it. I'd say polish up the art, as well. Things to think about for the future, not bad for a first game.