That lengthy, parallel development of engine and game was difficult enough that the company has found it never wants to repeat it, according to veteran Valve level designer Dario Casali. The history goes back to 2004, the end of a six-year span that saw Valve developing Half-Life 2 and its Source game engine at the same time.

So now that Valve has proven it can actually make a Half-Life game again, why hasn't it been able to make one with a '3' in the title? IGN delved into that question with Valve staffers in a recent interview that gives as detailed an answer as we've yet seen. But despite well over a decade of promises from Valve for a true sequel, Alyx's prequel storyline still leaves us hanging on Half-Life 2: Episode 2's long-dangling cliffhanger ending. Further Reading It’s been over a decade since Valve first promised Half-Life 2: Episode 3This week's launch of Half-Life: Alyx marks the first new release in the Half-Life series since late 2007.