If you are looking for an arcade shooter on a five year old engine then you may find some fun to be had.
I will begin by discussing the sp and special ops. Actually to me these are the best parts of the game. I will agree that the sp is more entertaining than the sp in bf3 but that is where the victory ends for mw3. The sp holds the same formula that it has had for 5 years but it is nonetheless fun to play through. Vetern difficulty has been tweaked to where it is actually fun instead of frustrating. The developers also brought back the special ops coop mode which is fairly entertaining. The most fun I had with the game was the spec ops survival mode. This is alot like the zombie mode treyarch has but with soliers, dogs, helicopters, etc. Judging the game solely on the modes it receives an 8 from me.
The problems with the game really take center stage when you play the mp. The maps are all so small and broken up that the strategy becomes run and gun and hope for the best. The sniping is mainly limited to point blank quick sniping...uhh not very realistic or fun. A knife is still better than a gun at close range...uh stupid. The akimbos return which is...actually funny but not very realistic for a war game. The latency is terrible in this game. What happens in your screen is not what is happening in your opponents. This is very frustrating. I guess though for all the whiners out there this gets rid of campers. So basically matches turn into players running around full speed looking for kills. The mp is so arcade like with very little stategy that I can't believe experienced fps players would continue to play this game. The killstreaks don't come into play as much which is a good thing. You can now choose from 3 different sets of kill streaks which adds some variety to the game. But this still doesn't make the mp fun when all the maps are baby sized.
Overall i can't believe this game outsells BF3. I guess there are alot of 8 yr olds with poor mothers. I am also not biased against this series. I loved cod4 and 5. But I also call a spade a spade. The cod series is dead to me until they reinvent itself like BF3 did with the frostbite 2 engine.