Get a few friends together, and knock out some AOE II. You can play this for 100+ hours with the right set of friends. Might be tough otherwise.

Magicka has a little learning curve to it. Once you can mash your spells out, it can only get more ridiculous. With the expansions, 30+ hours easy.

Mindless fun, 50+ hours easily. Just get some friends and shoot zombies in waves.

100+ hours of fun, possibly much more with the expansions. It has an open world making it better than other Sims games too.

Warband has a revolutionary combat system. Players can actually learn to play better from their experience playing the game. 1000+ hours

Borderlands 2 can provide players a great co-op experience, and 100+ hours of gaming fun.