The first time someone told me that I was using NGJ style I told them I only used the first person when absolutely necessary. My impression of the style back then was that it meant writing a first person essay pretending you are actually the avatar in the game. A little bit of digging and I found out that there were quite a few definitions of the concept floating around. It means rambling about yourself instead of the game. It means explaining the specs of your system and how your tactics worked. It's a gamefaq, it's fan fiction, or it's just a great story.
If you asked me now, I think I would just explain it as incorporating a discussion of the actual experience of the game itself into your essay. Which is simple on the surface, but much more interesting once people start really talking about the things they've seen in virtual worlds.
Kieron Gillen was awesome about answering any questions I had and Rock, Paper, Shotgun was an easy resource for finding quality NGJ work.
You might as well see what all the fuss is about.