Sorry for double post, anyway:
-Akimbo Weapons
-Better Spawns
-Some sort of Chatbar.
-Tactical Knife / Melee weapon(s)
-Parties (similiar to CoD), to be able to invite friends to your game etc.
-Multiplayer (Online)
-More games modes (Search And Destroy would be great)
-Instead of picking up weapons have custom classes to make.
DON'T:
-Make it 3, keep it simple, 2D gameplay.