After just messing around with NOLF 2 co-op for about an hour and a half with my girlfriend, I have to say it rules. It gives you a side story to follow after the main missions with Cate, which is pretty cool. Plus, the co-op feature is one that has been missing in games for a long time now. But it's back. And it's awesome!
Now, I know there's the teams in UT and UT2k3, which both games are awesome in their own right, but they don't have co-op like this.
All I need to do is train my girlfriend so she's not such a newbie. She's funny.
Definitely check this one out at a lan party. Great fun!