You've explained the appeal of the story very well. I have to admit that I'm not a fan of JK Rowling, for exactly the same reasons--I'm not much of a plot reader, and the flatness of the writing style just doesn't carry me along sufficiently. As for the characterization, I can sort of see it, but not feel it, if you see what I mean. It isn't to say either Rowling or this author are bad writers, just that they're not my kind of writer.

It's very interesting that there are distinct genres and periods of X-Files fanfic. I'm a new fan, so I wasn't aware of any of this. Personally I fall much more into the Penumbra camp, certainly as a reader and potentially as a writer though I wouldn't want to opine on whether my style is successful or not.