Here are some ideas for gamemodes in multiplayer.
Intel: There is a laptop somewhere in the map. The objective is to grab the laptop and hold it for as long as possible. The laptop carrier location isn't revealed unless a UAV is up. If he is spotted then his location is revealed.
VIP: Pretty much an assassination match. One team has to take out one member of the other team.
Informant: There is a hostage on the map. Your team must grab him and bring him back to your base. There are two ways to carry him. One is carrying him on your shoulders and which means you are defenseless. The other is putting your arm round his neck and pointing a one handed gun out. If a team kills the hostage then the other team gets the point.