One of the best zombie games around.
Simply put... wow. Incredible game, truly. I'll break down the review and offer a few tidbits of advise as well.
Graphics - Slick, smooth animation, as well as a very dirty and gritty Dawn of the Dead feel to it. The player avatar was rather very nicely rendered as well, though I found it just a little weird that the model was much better looking than the survivor/zombie models. Hardly enough to detract from the incredibly quality of the game, but it is something I found to be peculiar.
Style - Dawn of the Dead. I thought there was a very gritty 'oh shit, what now?' quality to the whole thing (especially that main menu). Furthermore, it's zombies, and zombies make things more awesome. Nonetheless, the overall atmosphere of the sound and graphics combine to make a very dark atmosphere that is well-suited to the game. Bravo!
Sound - The sound was remarkably good, all things considered. The only thing I found a little bothersome was that many of the gunshots seemed strange, or inappropriate to the weapon (barring the Barrett and the Chainsaw ^^ ). The sounds of the zombies was spot-on in my ever so humble opinion. I'd like to suggest possibly re-tooling some of the sounds of the gun-fire, though it is hardly something that takes much away from the game.
Violence - Shoot a zombie in the head, watch the head explode. Gory goodness.
Interactivity - Yes, it's a defense game, but there are a few little quirks that keep it from being just another defense game. I like the options for searching for survivors and weapons a good deal (and honestly people, besides food/weapons/ammo/people, why the hell else would you go wandering away from your fortress during a zombie apocalypse?), especially after reading both of those books by Max Brooks. I love how the aim shifts depending on where the character is positioned in regard to the aiming cursor, and those survivors are actually USEFUL! Imagine that, competant allies for once (Well, the final two survivors anyway).
Overall - Magnificent game, really, and I hope to see another, or more of this quality from you. The atmosphere and play style work very well together to create a game that is great for killing a few hours. Instead of more weapons, I would be happier to see a bigger difference between the weapons, as except for the hunting rifle and chainsaw, many of the weapons are extremely similar in just about every aspect (No clear difference between UMP/Uzi/AK47/M16 with the exception of the Uzi's giant clip). Besides, I found myself using the Hunting Rifle the entire time anyway. I would like to ask for some way to make some weapons more appealing than others for certain levels. I mean, why would anyone *Ever* take either of the shotguns?
One final note: the Difficulty. When I first started playing, I thought it was a small bit of a challenge, but it pretty quickly levelled out and stopped getting very difficult, especially once I had the hunting rifle, and all the survivors. Though, for everyone clamoring for harder difficulties... beat it with only the starting pistol first. Then you can ask for a harder difficulty. So... perhaps a variable difficulty level? ^^