I remember playing Half-Life Deathmatch in my Networking class in College. That eventually lead to Counterstrike,, which I played for years until I realized how much money there was to be made at sites like Party Poker and others with the poker boom that happened. But yeah, I would have to say because of that Half-Life has to be one of the all time great PC games just becausxe of not only being a great game itself, but due to how many other games were built from it.