Team Deathmach : The most common game, just kill all your opponents.

Capture the flag : Get the flag from your enemy's base.

Center flag : One flag in the middle... who will get it?

Counter Strike : One team plants a bomb and the other has to find it and defuse it.

Defend the Bus : One team stays inside the bus and has to defend their flag from the enemies.

... and many others, just leave your imagination go wild!