Left 4 Dead's world is a miserable one, no? Ruins and darkness and more ruins and zombies. What the game needs is a break. A break in space.
Mapper Aigik has come up with Contact, a Left 4 Dead 2 map that puts both zombies and survivors in a sci-fi setting, with fancy lighting, holograms and planetary bases. Like Metroid Prime, then, only without a suit to save you from the rotting jaw of the living dead.
You can grab it here, but be warned: in terms of both performance and zombie AI, it's not quite perfect.