I have it. Its cool but you have to play with friends or you just ends up playing with tards who does not have mic and just rushes on^^
It would be free, great con to get people interested in actually having the steam instead of using cracked copies. Afterall, once you have steam on your system might as well use the proper versions right? Just kidding - its a game made by enthusiasts using the SDK, and they must have got permission from them as a means of distribution, they probably thought highly of the quality? Completely guessing of course.