That's why I like Half-Life 2's story so much. First time I played it, and the Episodes, I got the main stuff. Then I checked the wiki and found SO MUCH MORE STUFF that I missed. I was like, "Wait, that never happened. What are they talking about? Where did they get this information? I don't understand..." So I would go back and play the game and look for all of this stuff and wow...and Yahtzee is right in that they can get away with so much because nothing ever seems to get nailed down. It's always just hinted at with everything, but never fully stated, so if they want to change something later, they can.
Such good storytelling. If only they didn't take so long to tell it. Well, whatever they do, I hope they don't reveal everything about the G-man. I want to know who he is, what he is, what he wants, and all that, but at the same time I'm fully aware that by giving me even ONE of those details, the Half-Life games will lose a massive amount of their charm.