Not quite to my tastes.
I'm reviewing this with a gamer's point of view. Which would be that's it's incredible. But my tastes just play hated it. No offense, you made one of the best defense games ever, but I find myself liking Last Stand a bit more, even though this one had more guns and you can actually run free in the area. The terrible annoyances I found were that there were no body shots, only head shots so accuracy was way to important here, how much health some of the fast, fat ones had, and the miniscule amount of exp. you receive for killing a zombie. I was on the 5 level or so and had only bought two other weapons. And when I tried to save money and not buy any upgrades, I'd get raped by some new zombie that's even more ridiculously fast, strong, combination of the two. If you could make the screen a bit bigger or make the zombies bigger, that would be good. And maybe give a little more exp. for each zombie killed. My favorite part about defense games is upgrading guns and then owning with my new weapon, droolingly anticipating a new one. But in this game, there was only upgrading. No owning. I don't like barely getting by. Because then I have to get my health back up and can't get a new gun.
All in all, I would advise survivors/partners, more exp. per zombie, a larger screen, and some more easily reached gun upgrades. I may suck at this or something, or I just don't have the patience, but this seemed a bit hard.