If you like FPS, get this game. NOW.
The co-op is very good. It's fun, a good cross between campaign and multiplayer and you can even unlock some weapons for multiplayer by playing it. There are only 6 levels, but they are all challenging and an extra fun piece to the game.
And now the multiplayer. If I scored the multiplayer alone, it would be no less than 11/10. It's addictive, engrossing and there are so many choices and freedoms. There are 9 maps and 5 game modes all of which are excellent. There are hundreds of unlocks and possibilities for guns, vehicles and equipment. How you play the game is 101% free too. In some shooters you find people, kill. Over and over again. In Battlefield 3 you heal and revive, resupply, drive tanks, helicopters, jets and more, shoot mortars (yes, mortars) shoot, destroy buildings and trees, repair, capture, set charges and more with a different experience every game. If you like big scale modern warfare, get it. Call of Duty may still hold the best singleplayer, but Battlefield 3 has by far the best multiplayer and maybe the best FPS to date.