Great stuff!
In my opinion, I think this is one of the best games on Newgrounds. I've been playing it for about an hour now trying to unlock all the survivor mode secret characters. The inlcusion of Kung Fu Karl was a wise decision and all the secret characters brings lots of replay value.
Now for the criticism: I think victory animations and more dialogue and sound would have made the game ever better. Regardless, it's an awesome game. Good job.