I was finding this fairly interesting, up until you tried to present the G-man as a vampire. Firstly, let's take a look at your definition of a vampire.
"looks human, but isn't; eternal life; abilities far outside human experience; revels in suffering and often causes many deaths. The outside evil who destroys without remorse."
Ok, that's a pretty vague description. There has to be 50 different kinds of monsters that could fit that description. A lot of people give Stephanie Myers crap for "getting vampires wrong" but at least she got the hole Undead bloodsucker thing down.
Then there is that G-man doesn't appear to fit most of it. Ok he definatly comes of as evil but I'm not sure how you came to the "causes many deaths" part. As fare as I can tell in HL1 you see him walking around every once in a while. Then in HL2 he seems to have even less to do with what is going on. You see him at the begging and the end and... that's it as fare as I can remember.
Also, even if I were to grant you that he is causing a lot of deaths somehow, and enjoying it, you don't need to be a vampire to do that. As for eternal life and abilities far outside human experience, I'm not sure what your basing that claim on. I mean Gordon Freeman, the character you play, looks pretty much like he did in the first game. At least in the artwork anyway. So it's not like the first HL takes place in the 1300's or something and then we skip forward 700 years. As for that bit at the end, Dr. Breen didn't seem to have any trouble using advanced alien technology why would you assume G-mans "powers" were magical?
Not to mention that Half-Life as a game is sci-fi and, to my knowledge, has no supernatural elements.
All in all I've seen nothing that would even remotely point to the G-man being a vampire, an alien conspirator maybe but not a vampire.
Other than that I thought the article was good.