As promised, Valve has released their new (and free for PC owners) campaign for their hit zombie co-op shooter Left 4 Dead. The campaign, Crash Course, contains new campaign maps along with new Versus and Survival maps. 10 new Valve achievements have been added along with some matchmaking improvements. Valve has also decided to put the game on sale for 50 percent off its normal price for the next three days. That means you can buy the full version for a mere $14.99.

Valve has decided not to release any media from Crash Course before today so it should be interesting to see what the reaction is from players now that it is released. Valve has pledged to continue to support the game with new downloadable content even as it prepares to release its sequel, Left 4 Dead 2, in mid-November.

Update: Valve has also lowered the price of the Left 4 Dead Four Pack. You can now get four copies of the game (one for you and three for your buddles) for just $44.99 for the next three days.