"Half Life is the best unfinished series, it's kinda like Volkswagen giving you a Bugatti in 2005, give you half the engine in 2007 and bits of the valves later on. With the wheels still missing. Then half a year later they give you two VW Golfs and completely deny existence of the Veyron at all...
...Goddamn you Left 4 Dead."
Valve's business policy.