I don't want to spoil things for the few out there that don't know about it (though I doubt they'd be reading this junk thread anyway, but better to err on the side of caution I guess) but it is a prequel and a sort of "sequel" that resolves cliffhangers that Valve was content to leave as is for so long while, in theory, setting the stage for whatever is to come next whether that's an actual third game or something else. Hopefully with this cliffhanger the public won't be left waiting another 10 years or more to see just where the heck the story was going. Maybe it'll even happen with no further unfortunate passing in the voice cast as well.