I just got this game, and I have to say its more addicting than World of Warcraft. The co-op is the best I have experienced in any game. The multiplayer for this game is literally the single player with your friends, the perfect mesh of all the single player gameplay, but throw your friends in and make the enemies tougher. "Wait, tougher?" you ask? Why of course! Why would they let you play against a LV 20 enemy if your whole party is around LV 18? You have to fight LV 26s or higher in the same area! But don't scream just yet, because tougher enemies leave better loot, and let me say, some of the bigger enemies leave behind some pretty sweet guns. It's sort of played like Diablo II except in first person with guns/rifles. You can even duel just like in DIABLO II
FPS+RPG= Borderlands. (Best game on 360). Better than Fallout 3 in my opinion. This game even has vehicles.
Replayability: VERY HIGH
OVERALL SCORE: 10/10.
Now, excuse me while I go play some Borderlands.