Does anyone like the Ghost Recon series of games? I'm playing Advanced Warfighter at the moment - its fun, but really annoying if you play single player with AI squad mates - the missions are quite hard like that. If you're playing co-op with a friend then its a lot of fun though.
Don't play it online, but I'm a big fan of the series.
I love the tactical element, though do agree that parts can get frustrating, especially when the AI squad aren't being particularly sensible.
I think that the latest iterations have been particularly realistic, and whilst it's difficult to pick up and play the game, putting some thought in at the planning stages can be very rewarding.