At Microsoft's X06 Conference in "Barcelona" they confirmed that the "previously unannounced major franchise" that was being released today is DOOM.

The XBLA version includes upgraded resolution, 5.1 support, 4 player split-screen, both local and online 4 player co-op as well as Death match. Unfortunately it doesn't support WS (although it does allow you to stretch the screen).

For those of you who are Achievement whores, here's the list.