I'm not sure if all of these ideas would work, but here they are anyway:
1. A fight set on a cargo plane. The plane is out of control and every once in a while, it flies down, entering a period of zero-gravity, in which everyone enters a mode like that which happens when you jump off of a building on rooftops.
2. Maps that change during the course of a game, meaning that even more epicness could happen. An example would be the plane from example one rolling over at one point.
That's about all i could think of. Tell me what you think, and whether it would be possible in the source engine