I just picked up the PC version of this game. I've only played it for about an hour so far, my initial impressions are quitw favorable. I never played the xbox version(because I don't have an xbox) so I can't compare, but 've read the PC version has some extra content.
There are supposed to be a few extra parts of the game to play through, and once you beat the game, you unlock a commentary mode where you can play through the game again this time listening to the directors commentary, much like DVD extras.
The game looks fantastic, every bit as good as Doom 3. It doesn't run as well as D3 on my system, unfortunately. The good news is the game supports widescreen resolutions I'd to post a few pics, but I can't cause I broke my digital camera over the holidays. I'll at lest try to put up a couple screenshots.
I'll have more to say as I play through the game.