Well...
1)Larger and more open maps. They did good with some maps, but those maps (Havana and Arrey for Blops) are far and few between, and the only rather good maps for sniping.
2)Inaccurate ARs at range. The fact that with a sniper rifle, a guy with a Famas can kill me from across the map in Arrey is so fucked up. I say give the assault rifles... hell, give all weapons, a limited range when in iron sights that the bullets will remain accurate, or even travel.
3)Multiple attachments. Bare with me, but I think that we should be able to have a Red-dot sight, dual mags, and a suppresser on an assault rifle at the same time. So allow for multiple attahcments (unless the noob tube is selected) and make each attachment added affect the guns ability, as having more attachments means more wieght, thus longer ADS and increase sway, which leads to...
4)Add weapon sway for ARs. Dont make it as major as for snipers, but add a little. For the heavier a weapon, more sway.
5)Remove insta-knife kills. Anyone who says they should keep this, no matter how smart or nice, is a fucking retard. The only one hit kill with a knife should be the same as in Reach, a long assassination animation (which would look cool in first person, think the knifing from Blops) that could be interrupted by another enemy teammate. and if they keep the knife, if a guy runs up to stab you, have a ability to counter this and reverse kill that fucker.
6)No controlable killstreaks, like AC130, Chopper gunner, or Hind.
7)This is something that I thought would be cool, but have a forth Perk category, called eqiupment perks. Choose one of these to get a piece of eqiupment. So you would chose the GL perk and get a undermount grenade launcher, or something like that.
8)keep the primary perk affecting your characters apperance, so keep that and expand on it, with the secondary and tertiary perks as well.
9)you can carry up to three weapons in SP and MP, think like MoH, where you have two guns and the sidearm. But in MP, you can only go out twith a primary weapon and a sidearm.
Thats all I can think of for now...