I have been playing MW3 online and I am iffy about it. I am not a huge fan of the maps at all. BF3 is sick though. Played that online for the first time last night at a friend's house.
I wasnt happy with the maps at all. But the more I play them, the more I realize they are very intricate. There are so many ways of branching and getting to the same spot. Some of them are not visually obvious to begin with. So, even though they are small, they have some decent scope. I suspect campers will have more difficulty getting away with their bullshit once the maps have been mastered.
Overall. Not bad. The campaign is pretty cool. Special ops is also fun. Worth the money I would say.