I played it for about 10 minutes, had to quit to do some actual work! But the secret is the same as would be with a real zombie invasion - protect your back and funnel the hoard into a kill zone. With only one way to reach you and only one at a time able to face you, they're easy pickins! :axe:
Jesus, that's fun. I got to level 2, but died with about 600 kills... hard to come by ammo and health resources.