Great Multiplayer, average campaign
Let me start by saying that if you are looking for value, BF3 delivers in spades. That being said, the campaign is fairly mediocre (I thought BFBC2 was better). The multiplayer offers more vehicles and a steady IV drip of unlocks to keep you addicted and coming back. If you're wondering if you should get MW3 or BF3, get BF3. BF3 also offers team deathmatch, spec ops, etc. but I feel the multiplayer gameplay has more variety with the classes, game modes, and devices.