Gametype: Deathmatch
Theme: A busted space station that is literally falling apart as you play
Textures: probably a mix of the ones from DM-Phobos and vortex rikers from Unreal 1
Music: firebr.umx would probably work good for this.
Extra description: I'm not so sure about the layout, though some neat things to add in could be a room with a wall that can be destroyed, which closes the doors to that room and gets all players inside sucked out into space (though its would eventually respawn). Maybe some collapsing floors and a sniper ledge that can be blown up could help the whole "falling apart" thing. Though there would still have to be ways to get back up to the main map. Decorations could include busted computers, corpses, and variaous broken pieces of equipment.