They just released a new trailer detailing the single player campaign.
Apparently the Russians are trying to invade the United States through South America, and they're developing some kind of biological weapon.
Naturally enough, it's up to the boys from B-Company to find out what that weapon is and help the U.S. Military put a halt to the Russians advance.
http://www.youtube.com/watch?v=SDEuNdYWT1oBefore anyone asks, the song is:
Artist: Queens of the Stone Age
Song: Millionaire