A bit late to the party, but here goes.
Firstly I'll have to admit to being generally a COD /MW fanatic. The story on MW3 was whilst still on the very short side, a step back in the right direction in that at least on Veteran difficulty there were moments (only a few) where it offered up a bit of a challenge. Nothing like the random unlimited supply of grenades that was WAW, but even so, it was nice to be slighlty challenged on what is after all suposed to be the hardest setting.
As for the multiplayer, I have to say I'm loving it, so far I've put in 97 hours online, and still not bored. However I do have a gripe, I paid up £34 (I think thats what it cost) for Elite membership which was to include 22 pieces of DLC. The problem I have had is that in January they gave us 2 new maps, February 1 new map, then March 1 new map + 2 Spec Ops missions, these were exclusive at the time to elite members only, but I normally only play 'hardcore' on COD / MW because I personally find you get less of the 'idiots' (though slightly more campers). The issue being that if you wanted to play these new maps they were only available on 'normal', well I played them just to see what they were like, but went straight back to 'hardcore' thus missing out on the benefit of having these maps early. It is only now as a 'map pack' dlc has become available to everyone that it has become available in 'hardcore' mode, I'm guessing that this is a problem that will be repeated over the coming months. Okay I know it hasn't dampened my enthusiasm for MW3, but as it stands, I probably won't being paying for elite again, instead just buy the packs as they become available to everyone.