zOMGies Make moar!
I want a sequel. Right now its a great start -- you have a lot of potential on your hands. Feedback I could give:
Better targeting system. (at least a big crosshair for a cursor)
Car/Truck Bonus Mode? (Your chance to chase down some zombies.)
Upgradable weapons?
Shifty McGriff Character Select?
Shooting zombies slows them down?
Visual warning for when barrels/explosives will come up?
Storyline?
Full screen mode?
Boss fights?
Just off the top of my head.
Keep up the good work!