Single player. One of the worse games I've played. It's really not a game, but a really bad, cheesy, interactive movie on rails which often makes no sense. There are more cut scenes than action and the action that is rarely little more than quicktime events. There are a few shooter sequences which are great, but they are so scarce, it's not worth the time. The only reason I finished this atrocity is because I'm stubborn.
I just removed the subsequent Call of Duty games from my Steam wish list.