I know it's a few years old now, but I just saw it for the first time a couple nights ago. As far as movies based on games go, it was a lot better than I expected. It strays from a few key aspects of the game (they aren't demons from hell, they're "mutants" affected by a disease) which was a bit disappointing. The first-person part of the movie, while a cool idea in theory, came across more like an amusement park ride. All-in-all though I'd have to say I enjoyed the movie, even with its flaws. If nothing else, it's a decent action flick.
The only interesting part was how they manufactured the entire movie; I could care less about the actual storyline and crap because I couldn't get into it. Knowing that they used 3d models for the entire first person scene makes me feel at home.