Interesting idea, too difficult for me. I got to wave 5, but at that point there was no way to get to my generator (swarm was all over the screen) so I was just running around. I noticed that the zombies would spawn on top of you sometimes if you were in the corners/sides which was kinda annoying. Maybe have an indicator before they spawn so that you can get out of the way or don't spawn them when the player is within a small area.