I'm not sure. In any case, I seem to have resolved the issue . . . I've stopped playing it.
I really liked MW1's MP, and MW2 is very similar, yet something feels different. I can't quite put my finger on it. Regardless, I've played it enough to find that I don't enjoy it that much, which I was not expecting.
I have a lot more fun playing H3 MP, or Firefight with Al and Brit.
Part of the problem was you were playing with a large group (bad) in TDM (worse).
My experience is that MW2 has a built in audience that is very good at the game. Players played a TON out of MW1 and before I even got the game I was seeing people with over 48 hours on MP online time. I am at 8 hours and level 25 and I am finding very few games with people ranked lower than me.
MW2 feels like Halo 3 did for me for a long time: People just knew the maps, weapons, and gameplay dynamics a TON better. It took months before I could even tolerate it.
I think the thing is about these well established MP games is they have a HUGE audience and you need to practice to have much fun as it is a skill based game. If you don't have the time prepare to be the cannon fodder. And that was always how CoD4 was on the PC: it is a BRUTAL game. People are NOT bullet sponges. If you take a bad step you are dead.
Some basic tips:
Use the map perimeter. e.g. move clockwise, keeping the center of the map to your right. be careful not to venture into the map too deeply unless you are sure you are clear. By doing this you keep the enemies forward and to the right--the map boarder forms a natural boundary to your left and if you continue moving your rear should remain clear-ish. Pick your engagements and try to ambush fire fights from the flank and, ideally, from elevation.
Let other charge forward. You are with 2 other dudes--let them press forward. They will be the first to draw fire and you can then take out the defenders. Unless you are great at rushing (Ostepop) allow others to draw out enemies and then you can flank and get the first shot off. More often than not they are focused on the rushers--and have emptied their clips and are reloading.
Reload behind cover. Common sense here... which I often forget. You cannot fire while reloading so you should do it under cove if at all possible.
Know your line of fire. When approaching any new path know what is ahead--is it open? A hall? What windows? Knowing the map and quickly scanning the firing lanes and hide-ee-holes will cut down on deaths.
Slow Down. Sprinting means you get your gun up slower than someone not sprinting. Likewise someone crouched and not moving has better hip fire than someone running and spraying. The tendancy is to want to run run run and run some more. Taking things slower and focusing on cover, elevation, and flanking the enemy while utilizing stun, flash, and frag grenades will give you an lot of multiple kills.
Even though I am still learning the maps and am only at 8 hours in my KDR this weekend went from sub 1:1 to well above it and my weekend was about 3:1 KDR. Not much changed, less Scott and I were chatting and I mentioned the above ... and tried to remember to DO these things while I was playing. I was being really undisciplined.
The game is brutal. MW2, like MW1, rewards players who have good fundamentals and unlike Halo there is a bigger separation between good players and bad players. With Halo you always had a certain amount of damage and being in a group increased your chances of pinging the shields--in MW2, if you and your buds make a bad move you can all be mowed down, repeatedly, within a second. It isn't that Halo doesn't allow triple+ kills, only that in MW2 you can do it with your core gun.
Interestingly I am NOT finding the air weapons a big deal. Cover is easy enough and now with Cold Blooded I can ignore it if I choose. The perks are nice, but they aren't as a big of a deal a lot of times. They more often than not give some extra momentum to the team that is already doing well.