Firstly, give us team tac back. Why would you want to take that out? I don't know how many times me and my buddies would play that on our friday night CoD sessions.
Secondly, remember back to Modern Warfare 2, when there was a 3rd person playlist? Yes, I think we need one back. Why? Simply because it adds something different to the game, something new. If you haven't tried 3rd person acog sniping, you definitely should, it's intense.
Thirdly and lastly, infected. Lately I play MW3 a lot (mostly because of the Blops2 lag crap) and infected is so much fun because I love hiding. Most entertaining thing is hiding in a bush that nobody knows and lasting the entire game. Why isn't there an infected playlist? I'm pretty sure it was more popular than hardcore s&d...just sayin'.