Well,
Having played the ass off this game when it came out on PC, I wasn't expecting much, but I was pleasantly surprised by what Vicarious Visions have managed to pull off.
First things first; Yes, the graphics are awesome. Every detail that was apparent on the PC may not have been ported, but most of it is there. I'd say it's about half-way between low and medium quality compared to the PC version's settings, but it also runs at a solid 30fps, with full shadows, and all the special heat/explosion effects are present and looking tasty.
Sound is just as good as PC (read: freaking awesome) and really helps with the immersion.
Ok, so most of the SP story has made the port, albiet with some slightly cut down areas, mainly to boost the frame rate, I'm guessing.
However, this game absolutly shines in the co-op mode, exclusive to Xbox. My flatmate picked this up on release date, as did I, and we litterally couldn't play anything else untill we had beaten down on Hell's ass, and completed the story. The co-op mode is broken down into seamless ‘chapters’ from the SP mode, editied for speed, and most of the areas have been enlarged to accomidate two players.
Downsides? The very basic MP mode (DM, TDM and some tourney modes) gets old fast, and is nothing compared to Doom3 MP on PC. Some textures have very noticable compression artifacts, which isn't great, but the Framerate stays nice and solid, so it's an acceptible compromise.
Essentially, if you havn't played the PC SP mode, or you have a mate who's keen for some Co-Op action, GET THIS GAME. On the other hand, if you HAVE beaten the SP mode previously, and you're not interested in Co-op, there's not much here for you.