More specifically, the dialogue between M&S sounds like an episode to me, in the best way. P's Mulder always seems slightly in awe of Scully, even when he's ticked off or annoyed with her.

I didn't realize it until you pointed it out, but this is so true, and one of the reasons I love her characterization of Mulder so much. And this time around, her Scully was pretty spot on too.

I was, I admit, a little leery of the "horror" description, but it's not Friday the 13th/Halloween type of horror, but a more realistic (and maybe therefore in some ways even more horrible) than those types.

I rarely read horror, but this story was the kind of creepy that I like. I think you're right about about it being more horrible due to its realism, though. I also think that having the story set in a middle-of-nowhere asylum allowed readers' imaginations to fill in the mental picture to the fullest horrific extent - we've all seen shows or movies with a creepy haunted asylum and we can take the descriptions we're given and envision whatever we find most frightening following Mulder through the asylum...