Five pages in and no one has mentioned Payday 2? It's a four man crew game that rewards teamwork and communication. Been having a blast playing with my GoIO crew.
Yes, the AI is a bit atrocious, and the game is fairly repetitive, but these are things that a GoIO veteran probably isn't opposed to. The grind factor, half-crafting system, and the somewhat random nature of each map spawn do help to alleviate some of the repetition.
Then again, I'm only about 10hrs into it, and still very low level. Perhaps it will get boring quicker than I'm expecting.
Seriously, though, for $30, it's a great game. (Friends required, sold separately.) It's still new, but when it gets a Steam sale, there is no excuse for not picking it up. Runs like butter on my oldish system, too.