Looks like Doom is the unannounced XBLA game that MS mentioned last week.
http://www.360monster.com/newspost.php?id=0000001244
http://www.360monster.com/newspost.php?id=0000001244
The original Doom is rumoured to be seeing a release later today, with a much higher resolution, 5.1 sound, 4 player split-screen co-op, and on and offline multiplayer, all for the comparitvely low price of 800mp. Whilst this may seem a bit disappointing to some who were expecting a new IP, I'm sure the multiplayer and achievements will be enough to sway a lot of people into buying it.
http://www.xbox.com/en-US/games/d/doomxboxlivearcade/default.htm
- Gameplay: Experience all the classic DOOMand DOOM II levels, monsters, and weapons. Play the entire single-player game solo or in co-op mode via split screen or over Xbox Live.
- Multiplayer: Play up to four-player deathmatch, either in split-screen or on Xbox Live. Earn achievements and check the leaderboards for the high scores.
- Next-generation features: With 1080i HD support, 5.1 Surround Sound, and smooth textures, this is DOOM for the next generation.