As previously reported here Valve has announced that the new DLC for the original Left 4 Dead will be available in September. For 560MS points, Crash Course will add a new campaign and some Survival maps.
As per Valve:
“Crash Course” bridges the gap between the end of the “No Mercy” campaign and the beginning of “Death Toll” in the original game, expanding the game universe with new locations, new dialogue from the original cast, and an explosive finale,
“The primary goal of “Crash” is to deliver a complete Versus mode experience in just 30 minutes, resulting in a streamlined version of the game’s existing Versus campaigns.”
Versus will also get a respawn timer so you can see how long you’ve got before people respawn, and the item drops have been adjusted.
