This game's first impression isn't too good. The levels are very drab; of course this is partially on purpose -- the game wants you to feel all the decay of its locations -- but some of the textures are so "illegible" that you can't even know what they represent, even for a 2005 game. And the geometry of such levels isn't inspiring either -- too many small rectangular rooms, especially in the first level, connected in strings which feel like a huge, twisted corridor.
On the other hand, using small rooms with lots of sharp turns provide plenty of opportunities for enemies to scare the heck out of you in close combat. You see, most of the combat is melee, using pipes, axes and whatever you find around, and your walking speed is rather slow. When you find a firearm, usually with just a few rounds, you cherish it, and save those precious bullets for just the right occasion. This is actually a bit annoying -- you can only carry ONE weapon at a time, forcing you sometimes to go backwards to find a better weapon if your runs out -- but adds to the tension. Also, the AI of enemies is interesting -- they sometimes hold back and wait for you behind corners (sometimes pathetically, but it actually fits their rotted-brain profiles), which forces you to be even more careful.
Talking about tension, the star of the game is the sound design -- it is always just noticeable, adding plenty of atmosphere and keeping you on your toes even if nothing is actually happening on screen. This is more of a horror game, with action and some investigation thrown in.
Yes, the investigation bits: the gadgets are quite smart (a later level uses the UV flashlight to a nice effect), and submitting info to your lab companion provides a natural way to get a little exposition for the story. They were quite easy, but very enjoyable.
Unhappily, the story is slightly muddled; there are some nice ideas, but many threads are left dangling, and the end feels a bit contrived. Also, the plot suffers from "why-the-heck-is-this-intelligent-character-doing-that?", which is very common in all media, to be honest.
All in all, an enjoyable game, which deserved better level design and a more fleshed out story.
Score: 75/100.