Good game
A good defense game here, some problems though, like the machineguns can begin to fire before you've reloaded wasting ammo and not doing anything. Also, sometimes the bullets pass straight through zombies without affecting them. I like some of the simple touches such as the diary and sticky notes. As the last guy said, how about some upgrades for weapons? Or how about a variety instead of different types of the same weapon?
Grenade launchers, flame throwers, mines, how about upgradable defenses as well? Also, how about a survival mode? Basically unlimited days but with more zombies each day.
Oh, and one final glitch, one of the riflemen of the survivors has no gun and does not fire... other than that, great game!!!