They Should Learn From Previous Cod Games E.g MW2 and WAW
1.More Guns WAW didnt have enough guns.
2.Pro Perks (idk if its copyright but i like that in MW2)
3.Sniping (failed in waw)
4.Stop Modding (i know this is a modding website but it killed it on MW2 All the leaderboard hacks where just annoying and 10th is annoying why not true skill? PATCh THEM
5.Zombies or Whatever (Plz Bring Zombies Back Or Zombie Related Back Co-op.
6.Less KillStreaks Notice how not many people camped on Cod4 or WAW its because they camp to get killstreaks good idea but id rather less campers.
7.New Gamemodes
8.Patch Modded Controllers (everyone on WAW uses them thier boring)
9.A Good Campaign I havent realy liked any cod campaigns yet compared to gears etc.
10.Customizations e.g (player looks,Camos(plz), Vehicle Unlocks etc.

These Are Just Some Of My Ideas / Opinions Please Comment And Add Your Ideas