Warhammer 40,000 Space Marine isn’t going to be having a cooperative campaign, just a “horde” mode. Taken directly from Gears of War, it features repeating waves of enemies that players must take down as one of the three available classes, Tactical, Devastator or Assault marines.
On top of this, as Relic have previously said, this coop mode won’t be coming out with the release of the game, but will be made available about a month later for anyone that bought the game new. Undoubtedly only those that purchase the game brand new will gain access.
Relic and THQ have said that all experience earned during the defence game mode, will advance you in the single player and multiplayer modes also. There will be two maps to slay enemies on, known as “Assault on Hab Center Andreas” and “Escape from Kalkya Facility.”