One thing most multiplayer modes seem to be lacking is a grand finale. In deathmatch, capture the flag, king of the hill, and control points modes, tension does rise as one team nears the necessary score or time is running out. But the game ends with no special event. Whether by holding a control point or getting the last headshot, the end feels basically like the beginning.
I enjoy those traditional modes, but I'd like to see a mode or two in which each match ends with a bang. I'm sure there are countless ways it could be done, but I'll try to offer a quick example.
The first scenario that pops into mind is teams of players racing and fighting to reach and fully control a bomb shelter, then nuking the other team.
Unlike Left 4 Dead, all members of a team must be present in the shelter and all members of the other team must be expelled from the shelter before the doors can be shut and the nuke detonated. Both teams would begin away from the compound, each with various spawn points on all sides of the map which are close to enemy spawn points. That splits the mode's goal into two: (1) reach and enter the compound, (2) defend the compound until all allies are in and expel all enemies. I don't doubt that the latter concept would need to be adjusted significantly during the prototype phase of design.
Since I love dynamics, I'd add plenty of environmental factors: neutral NPCs (aggressive or territorial), traps, etc.
The game ends with the shelter doors being quickly sealed. The nuke detonation wouldn't be a cutscene or long, but it would not be instantaneous either. That way, the teams have time to savor and dread the moment. It would look something like the detonation scene in The Sum of All Fears:
See what I mean?