all games are not created equal

Focusing on coop features, L4D totally rocks.  It's exactly the kind of experience I would want out of a coop centered game.  It's awesomely frantic and a ton of fun when playing with friends.  The coop is simple, but it's the environment and style of the game that makes it so fun.  And without your 3 other friends, there would be absolutely no hope in fighting off those 50+ zombies that may start coming after you.

L4D is kinda repetitive in the sense that all you do is shoot zombies until they die, then find more of them and kill them.  But what L4D does right is maintain that feeling of 'holy crap, there are a ton of zombies and we are totally screwed' through every level of the game.

Army of Two was a sluggish Gears of War type game that I don't think did anything right.  The buddy system sounded cool, but really didn't give it anything extra for me to want to keep playing it.  And coop was the focus of the game, so it's sad that I didn't find the main feature of the game intriguing at all.

L4D keeps calling me back to try and beat a new level under the hardest tolerable difficulty.  I can feel it calling me right now...