Named Game of the Year by over 50 publications, Valve's debut title blends action and adventure with award-winning technology to create a frighteningly realistic world where players must think to survive. Also includes an exciting multiplayer mode that allows you to play against friends and enemies around the world.
Free to keep when you get it before 20 Nov @ 12:00pm.
The game is likely to be made free for the upcoming anniversary, and they accidentally made it free early. They have since fixed the accident.