I like the idea that the zombies get cut in half on the first hit. On the other hand, those halves can still damage you, so it's a tough game to survive a longer period in. I guess it takes some time to get used to the very retro four-direction shooting, even though it works really well, and so makes playing easy even when you don't have a mouse at hand.
I'd like to invite your game to our contest, the Game Development World Championship!