Half Life doesn't really have a plot. I love the game to death (the first one, second one kinda sucks) but it uses obtuseness as a replacement for plot, much like the tv show Lost does. What it does is take something really simple and obvious and then obfuscates it. This can greatly help affect the emotional feel of a work - Silent Hill and Lost both benefit from it greatly - but we mustn't confuse it for actual plot development. Ever see A Christmas Story? "Be sure to drink your ovaltine".

But videogames aren't about plot - even adventure games - so, it's kind of a moot point anyway.