The main goal of Badwater Basin (for L4D2) is to create payload map that is fun, short, and informative. I don't think I've met most of those goals (it's definitely short), but I expect to refine the map as I get more feedback. The use of TF2 visuals is a side effect: brush work had taken up most of my time and I wanted to release something that would allow me to experience actual game play and player feedback. Just as Valve released their source to help community mappers, all of my efforts with this campaign would be pointless if I didn't release the source in a similar fashion. I'm not sure if the L4D2 mapping community will find this example campaign to be valuable. I hope it does!
The current version (Dev 3) is still primarily for developers and testers, but the tiny campaign can be finished from start to finish without any "show-stopping bugs" (and getting trapped in the Red spawn point is no longer an issue, I think). Thanks!