To quote my review:
"The co-operative is, in my opinion, the best part of the game. There are three classes to choose from: Soldier (a tank character who deals decent damage and has a shield), Special Ops (Deals the most damage, and throws ammo), and Medic (Doesn't deal much damage, but heals the team). Every game needs at least one medic, and one spec ops. That can work, with two people. With eight, you'll need at least one medic, one spec ops, and two soldiers. You gather Intel (which doesn't do much) and Grey Tech, which unlocks new gear for you to use. You also earn new weapons to use for secondary fire (ordinarily, the Soldier has a minigun, the Spec Ops has a battle rifle (best way I can think of to describe it, think of the one from Halo) and the Medic has a healing gun).
But, there are only three classes, which means there's quite a lack of variety. Also, the only story is a giant wall of text while the level loads. You won't read it. Nobody ever does. And you don't need much teamwork, either.
The competitive is pretty standard, and leaves quite a bit to be desired. Other games in the genre do it much better, and the only thing this has over several of those is that it supports two player splitscreen. There isn't much else to say, really."