It was horrible, mostly. They did an excellent job on the sets ? they look very much like the demo level of Doom 3. I would certainly have liked to see far more of the UAC facility, though ? they concentrated on a small portion of it, backtracking and re-using the same rooms repeatedly, instead of exploring deeper and deeper, as you would in the game. They never go beyond one small section.
People have been wondering if they would face the same four demons over and over in the movie, like they do in the game? well, I am sad to report, they only face two types of demon (not including the zombies), and one of them is unique. Not only that, but the monsters were not remotely scary; they do not startle the crap out of you, and they do not look especially gory, either.
There was a small section towards the end that was filmed first-person? it was only about 5 minutes long, thankfully, as it was probably the most horrible part of the movie ? it completely destroyed what little atmosphere and scariness had been there. It was, though, oddly amusing ? it made the entire theatre laugh aloud as the guy plowed through dozens of zombies.
The lines are disgusting, they changed the story pretty dramatically, and it was? overall? just like the game: pretty boring.