How did you find the difficulty? Some are saying too hard ... others too easy
First time I got killed by the first guy, and thought it was gonna be to hard. But after a while I started learning the game- that you have to keep the bad guys at a distance, but not too far, because you'll wanna eat them afterwards :) That the game rewards well aimed shots, and not spray and pray. That you can sort of kite the baddies together, so you have easier time targeting multiple new guys.
I can see it as a bigger game. Make the enemy waves limited, maybe add some upgrade system between them and you have a nice little wave shooter going :)