Who is this "mutual friend", the GMan? Did I miss something, does Eli know about the GMan? The way I understand it, the GMan saved a young Alyx from Black Mesa. And I can't wait until episode 3 to see these, "unforeseen consequences." So many unanswered questions.

I do believe the "mutual friend" the G man speaks of is Eli Vance. I could be wrong having never played fully Half-Life. *Stupid hardware limitations*

Yes, Eli is talking about the "G-man".

He's obviously kept in touch with Eli, fairly closely.

And you'll notice that Eli refers to him as; "Our mutual friend", but the title of the chaper is actually "Our mutual fiend".

Trying to tell us something?

And he mentioned the crystal from the first Half-Life. Obviously the GMan planned this whole thing. Or his employers. I wonder if the mystery of the GMan will later be revealed.

I think that he's part of an alien species moving behind the scenes in all of this to test the limits of the human race. I only derive this from his struggling speach pattern, and the fact that he only pops up in the most crucial of moments to actually speak to you.