In MW3, there should be alternate faction game modes.
There could be a SWAT v. Terrorist game modes, one where you have to secure hostages within the time limit. There could also be one where you have to defuse bombs in random places.
There could also be a Mob v. Mob game mode, where you fight over money stacks placed around the map.
In these modes, you'd have 3 custom class slots separate from your regular ones.
These modes would have different guns than regular multiplayer. They'd also have different ranks.
Give me some feedback.