The PC version of first-person zombie slaying game Left 4 Dead will be free to play this weekend. Beginning Friday at midnight, you will have 24 hours to experience the joy and wonder of single player and online, co-op Left 4 Dead on your PC.
Letting gamers play this title (and the "Survival" DLC!) is like a drug pusher giving potential customers a taste of the product; I defy anyone to spend a day playing Left 4 Dead and then not buy it. Very sneaky, Valve, but I am on to you, buddy.
You can pre-load everything you need to play right now, at the source link.