A 5 -- and that's only because I can't give it a higher rating.
Shocking, scary, creepy. Donnie Pfaster is a truly great villain (too bad they had to ruin that in "Orison"). Nick Chinlund did a FANTASTIC job with this character, who is indeed evil personified, "the devil in a buttoned-down shirt". He appears almost meek and harmless and yet, evil just oozes form his pores!
I like it when TXF educates me: the class on the meaning of fairytales was very interesting. I just love it when this show proves it's so much more than scary stories.
Scully's therapy session was characterization at its finest. Scully is a strong woman, but all the traumatic events she sustained (her father's death, her abduction) are now beginning to take their toll on her. She is acutely aware of that -- she hates it when she feels vulnerable. Scully is trying to regain her inner strength, not just for her own sake, but for the sake of the people she has sworn to serve and protect from the predators of the world. She wants to appear invincible before Mulder, she hasn't realised yet that it's OK for her to drop her armor around him. That's why it is so powerful and heartbreaking when she breaks down in his arms. Mulder is as shocked as we are to see her scared, but in this episode he is so caring and gentle and protective. His "I just don't want you to think you have to hide anything from me" moment is pure beauty. DD works miracles when he whispers and this scene is one of my favorite in the entire series.
Nothing happens in contradiction to nature, only in contradiction to what we know of it.