Co-op is just plain amazing but singleplayer isn't near as good (Very Minor Spoilers)
User Rating: 9 | Army of Two X360
The campaign, while a little short is VERY fun when played with a friend or even just a random player online, while singleplayer with the AI partner isn't near as good. The competitive multiplayer is very good as well and is based mainly on completing objectives (AI enemies are also spawned to defend these objectives) then actually fighting the other team, and can be very fun, my suggestion is that if you enjoy co-op and have other friends who can play the game with you then you should definitely buy (or at least rent) this game. While if you don't have any friends with a 360, or they just don't want the game, be warned that the AI partner screws up sometimes, and just isn't as fun, but thats true of just about all games that have a co-op feature. The story is pretty good and starts out with Rios and Salem training in the Army, displeased with the army they quit to join the SSC Mercenary corporation, and the story starts out with Rios and Salem just working as mercenaries as conspiracy begins to unfold
Graphics: 9.0
Gameplay: 9.5
Multiplayer: 10.0
Singleplayer: 7.0
Story: 8.5
Total: 9 / 10 
