Call of Duty: World at War allowed players to progress through the campaign in four-player cooperative mode. You'll be going it alone in Modern Warfare 2's campaign, though.
“We don’t do co-op in our story because we’re crafting a very specific experience and we don’t want to ruin that by cramming co-op into it," Infinity Ward community manager Ryan Bowling told Videogamer. "We take the moments that work really well with co-op, we bring them out and we put them in Special Ops.”
The Special Ops mode allows you to play alongside one other player. It sounds sort of like the competitive co-op from World at War in that you're being challenged not only to complete a level but to complete it well. "There (in Special Ops) it’s all about fun. It’s about playing over and over again, getting a better time – you’ll have a time at the end of it – it’s about challenging a friend going in on co-op and trying to beat it on veteran.”
"Two player seemed to be the magic number for co-op," Bowling said when asked why the game didn't have four-player co-op like WaW. "That’s when it stayed really fun and intense without becoming a clusterf**k of things. We just found that two-players was the most fun.”
Fair enough. As noted in our WaW review, four-player co-op did get a bit too easy at times. Judging by the sales for that game, though, it seems like lots of people didn't have a problem with it.
Modern Warfare 2 will be released worldwide on November 10th.