The developer said, “It’s gray box, and some code features are missing, but it’s playable from beginning to end, It also includes two standalone survival maps that never shipped.” You can either use the Automatic method ( unzip .vpk file and double click to launch) or Manually install it by copying the file in the Left 4 Dead addons folder. According to the release notes following are some known issues,
- Fire, smoke and explosions do not trigger panic events in the hangars.
- Zombies do not crawl all the time in the orchard.
- Farmhouse mob does not spawn in the far side of the woods.
- The covered bridge does not collapse with explosions.
- Burned forest area is missing wandering fires.
- The dam spawn room is missing health kits and weapons.