Okay... something's messed up with the newest (2.0.8.1) update.
I've installed it and then reapplied the re-emu (both the "2054+" and then tried the "rev-emu 2.0 epc edition") both with no luck.
left4dead2.exe shows up in my task manager for about 10 seconds, then disappears. The game never starts.
I then reapply the last update (2.0.8.0), and it starts the game no problem.
WHAT'S UP WITH THAT???
-UPDATE-
Okay... NVM....
The "sfk" version I got from the tunngle site was the issue.
It's different than the 2.0.8.1 update from here.
Installed the "L4D2_v2.0.8.0_To_v2.0.8.1_Update.exe" and have had NO PROBLEMS.