Oh, and the theory about Freeman being G-Man is ridiculous. There are no valid arguments to back that up either, aside from vague physical differences that are enhanced by swapping body parts in MSPaint. Hell, I could make Alyx look like Gordon if I wanted, just give her glasses and a beard. Not only that, this explanation of his identity strikes me as very very very immature. Not like something Valve would do, something a fan would make up.
Since Breen tells you that your services were open to the highest bidder, it would make sense to me that the G-Man is contracted to manipulate certain individuals for their benefit. After snatching Gordon up, it's understandable that the G-Man views him as a very important asset, being the powerful history-changing individual that he is. In this same way, he seems to be manipulating others as well, which would lead me to believe that Gordon is not singularly important to the G-Man, he's just a very capable person that he's being paid to control.
At the end of Half-Life 2, the G-man seemed very satisfied, as you had completed the mission you had been tasked with. Unfortunately for him, at the start of Episode One, the Vortigaunts rescue you from his clutches. At this point, Gordon is effectively out of his grasp, which was not what was supposed to happen. Somebody wanted you to disappear at that point, but I don't think it was the G-Man. Unlike the Vortigaunts, he doesn't seem to have any personal interest in you. He's just doing what he's told.