That was a bit hard to watch. It's a non-supernatural vampire story, with gross things being done in a cult. Just being in that grotty little apartment would make my flesh crawl. The tone's what makes it ewwww. The X-Files's tone is realistic, not (usually) camp or larger than life.
Personally, I think this is what vampire stories should be. I approve. I just wouldn't recommend this episode to my mother.
The themes are interesting. There's religion, especially since Scully's a Catholic. (That surprised me, but apparently it's been part of the lore since the beginning. Crumbs.) The episode's also about ageing, with Mulder getting sensitive about his "Definitely Not Bifocal" glasses, even though he often wore ordinary glasses in the original series.
I'd been a bit nervous about this. As it's ep.9 in a ten-episode season, I'd been afraid of another mythology episode. Fortunately, though, I was wrong. It's just revolting and horrible, which is much nicer.