Some quick thoughts thus far on my multiplayer experience:
1) Partys blowing up - no matter what we try, no matter who hosts, we get about 10 "The Party is No Longer Actives" for every 1 time we successfully get into a match. We all DMZd our xbox's just to make sure it wasn't people's routers and whatever. Same thing, no matter who hosts. Generally, is more problematic with party having greater than 3 people/
2) Blurry textures not just at the start of a map, but even as you move around, respawn etc. You pretty much need to be standing in an area for 5-6 seconds before an objects textures still sharpen up (many cases)
3) No footsteps. Getting knifed out by dudes with M60s, sneaking up on me with Tactical Mask or something. People without ninja move as silently as people with ninja. I can hear my own footsteps when I run, but not other people's around me. I don't hear anyone's gear rattling. Nothing. I have ninja pro unlocked, I have 7.1 surround, I have the in game audio set to theatre/loud... I hear footsteps in other MW games.
4) Spawn system is a bit steamy. People spawn in bunches behind you. Not so bad once you learn to expect it.
5) Sniping is a bit *too* nerfed. Quickscoping is basically gone (yay) but so too is normal sniping. People are not diggin the zoom bounce. My solution? Take out the bounce, but increase the aim down sight time of the sniper rifle.
6) A little too hard to kill people on normal. Full or near full clips required it seems, more often than before
7) Remote control cars getting tiresome
8) If you catch someone close quarters coming around a corner and have 3 bullets into them, YOU are at a disadvantage. His knife will trump your bullets every time. IMO if you are taking bullets, you shouldn't be able to reach into your pocket and pull out a knife, much as when you are taking bullets your are unable to properly aim and fire your gun.
Positives
1) Noob tubers less prevalent
2) Point blank Quick Scoping is gone (days of sniper rifle trumping SMGs at 25 yards are gone)
3) Kill streak rewards less rampant. Airspace less crowded
4) Less frustrating game play, over all.
5) Taking out the deathstreaks, and the silly perks like commando and other schlockery has really improved the enjoyment level for me. (flash gorden running around at the speed of light, pommol pistol stabbing people is gone)