First and foremost, I want to see Ghost/Assassin removed, I rely on both look around for people, and the minimap. Why the hell would you give a person an incentive to camp in a corner? If ghost/assassin wasn't removed, then at least bring back the blackbird to penetrate it so you know if you're running into a nest of ghost campers, or disable silencers when they use ghost/assassin. Better yet, make the ghost/assassin perk as an equipment instead, if you want to remain invisible to the UAV, and whatever else you have to place something like a Blops Jammer. For everyone that SCREAMS "Stop spamming the UAV", they should take Ghost/Assassin out, and make the UAV a 5 or 6 killstreak. I still remember mostly snipers using it in W@W, and it wasn't too big of a deal.
Another thing you should do is kill the rapid fire already, especially with the SMGs that are OP already. Also DON'T put double tap/rapidfire on Assault rifles, that's one of the worst ideas in MW3. Had they made the gun they put rapid on shoot normally, there wouldn't be a need for it at all, I can shoot the single burst rifles perfectly fine/fast without rapid fire equipped and win 92% of my gun fights, just like many others, why put rapid fire on them?
Bring back a LARGE assortment of single burst rifles, I loved all the single burst of W@W, and Blops, I'd love to see the W@W ones back. Also wouldn't mind scopeless snipers again like what we had in W@W, they were great.
If you bring back Gun Game, take OUT the humilation, it's annoying as hell getting to the last gun and oops, you just got demoted from someone stabbing you in the back. Also to prevent people from camping mix Gun Game with Kill Confirmed so if they want to upgrade to the next weapon they have to get to where they just killed the person and collect the new gun. Make it so if someone gets to it they get points, NOT the gun, and the person who earned it has to kill someone else for the next gun they need. Also do the same thing for One in the Chamber, they have to collect the bullet from the person they just killed, or the kill doesn't count towards the final score.
Don't change the killstreaks AI, MW3 is far too powerful for their killstreaks AI, so you have to camp indoors to prevent an insta-death from out of nowhere. I'm not saying dumb down everything, but don't make it so that the first two shots from an attack helicopter brings you down. BlOps had it right, the unmanned killstreaks were powerful, but you could survive more than 2 shots from it.
Also fix drop shotting so you can shoot while you switch from stand to crouching, or proning, or make it realistic. Go out to a shooting range, and have an expert dropshot and use what he does to model the game's drop shotting after. If the gun goes crazy while the guy switches to a crouch/prone, then incorporate it into the game itself