A decent time shooting things up with a buddy. Not great, but not bad.
Graphics aren't half bad at all, but nothing amazing. Some texture issues, but customizing your armor is a very nice touch. Guns feel fine, not over the top but it doesn't feel like your RPG is shooting pebbles. Controls are easy to get used to.
Storyline isn't anything original, but it gets the job done. It won't drive you to play the game, but it also won't matter.
AI is average. Enemies will take cover, occasionally try to flank you, try to blow you out of your cover, but allows your partner to easily flank and take them out providing you use the aggro system.
Gameplay is based around the idea of "aggro" or aggrovating your enemy to the point that he will lose sight of everything around him except for what is firing at him. This gives the game a reason to play with two people, one to take the heat, the other to attack. Not using this to your advantage will make the game difficult, but not impossible by any means. It *will* make the game seem extreamly easy when done right.
Replay value is pretty low being there arnt' many unlocks and the game can be beaten inside 5-8 hours. There is a versus mode, but not many people play it and its very cheap. Some weapons are extreamly overpowered making the others useless.
In the end, the game is a good time provided you don't depend on the single player for its fun. With a buddy and a weekend, you can have a blast and return your rental with a good experience. Its worth trying, but not worth buying.