This is one of the best games I've ever played here on Newgrounds.
One of my favorite things about this game is that it appeals to all playing styles. For example, in the beginning of the game, I stuck to using the Shotgun for everything, had it fully upgraded, and it was fun. Then I fully upgraded the Sniper Rifle, and noticed that it was just as much fun, but in a different way. I think that adds replay value and makes it fun for all types of players.
I also like how the different zombies actually feel different when you're fighting them. They don't just feel like they are the same character with a different skin, they each have their own style for fighting them. For example, to be successful you really have to fight the zombies who throw explosives and the ones who just use guns in a very different way. It's not that it's more important to take one on over the other, but they must be fought with a different methodology.
The graphics are beautiful and fit with everything else in the game quite nicely.
This game is simply great.