Having played this game solidly for an hour and a half, I feel that I'm now able to write an honest review.
This is simply incredible.
There feels to be nothing missing in this game. The graphics are polished and crisp, the user interface is friendly, and the controls are very easy to pick up and use right away. The character animations are near flawless, and I particularly like the death animations, they definitely set this game a cut above the rest.
The ambient soundtrack is immersive, to say the least, with the different sounds of the world mixed in slightly to create a very eerie and threatening atmosphere. The weapon sounds are excellent, too. The shotgun in particular is satisfyingly meaty, and the accompanying result on the zombies only helps that.
The gameplay, though, is what really sells me on this. It would've been so easy to leave this as a straightforward 'kill the bad guys' game, but no. The strategic components are very well thought-out, upgrades in particular shone for me, as I found myself often trying to balance between firepower and auxiliary support (such as income, sprint rate, health regen, et al).
The cons for this are simple.
1) as stated before by a few reviewers, the game is rather repetitive, and I do feel that another music sample may have been used for combat with large groups of enemies, something a little bit more metallic, to really get the adrenaline flowing. Although, I can see why you didn't, as it may have disturbed the overall atmosphere of the game.
2) The window for this game was much too small. Not to the degree that it would've rendered the game unplayable, but just enough to annoy me.
All in all, this is simply incredible, and I don't know why the hell this isn't on Steam.
This needs to be on Steam.
I'd buy it.