A new mode in the game, called Special Forces, will consist of a number of isolated stages not tied to the narrative. There was no indication of precisely how many of these Special Forces stages would make it in, but according to Game Informer it'll be a "major part" of the game. More interestingly, while the story campaign will be single-player only, the Special Forces maps will allow two players to run through co-operatively.
Details about Modern Warfare 2's multiplayer element were scarce, though Infinity Ward told Game Informer it wanted to emphasize making players famous based on their accomplishments in matches.
For more, check out Game Informer issue 194, or head over to our Modern Warfare 2 object page.