I made blaster rifles that shot destructions, but never realized you could shoot map features. That sounds like the potential for interesting fps: remake the map as you go.
You start the game, and have 2 minutes to create defenses. After that, it's a normal game of CTF.
I forget what it's called though.
http://tvtropes.org/pmwiki/pmwiki.php/Series/TheATeam?from=M...
See: http://www.worch.com/portfolio/wot/ for a description of the planned vs implemented Citadel mode.