Really good, but...
First let me congratulate you on a job well done. This game had me enthralled during the entirety of it. By the time I noticed the time I was well into it almost an hour. The music was well thought and placed and just seemed to pull you into it. The art gave it that contra arcade style to it that kept you playing.
As for the vague clues and map, I have to say they were perfect. It was as if the hero was going in with just whatever knowledge and recon that was available. In a true zombie situation, even if it's a publicly well known floor plan/layout, you will never be able to get 100% of the information.
As for the no upgrades: I actually liked that, as I find it doubtful in such a situation that there happens to be the same vendor to sell you specific upgrades to your stuff every so often.
Only thing though is that it seemed to be glichy and slow at times. I believe this is more then likely that we (including myself) may not have either the latest flash installed, an out to date graphics card, or a combination. Adding a quality button would make take care of that and make it play smoother.
Also, one last thing that was a slight let down. In the intro it showed a monster sized zombie rat that looked like it could make a grizzly bear run away in fright, yet it was no where to be found...
But anyways, to recap: awesome game!