1) why do I love the HM?
I love it because of the lavish set-piece that it is. The theming and attention to detail are top-notch. I also love it because it terrified me as a kid and I am obssesed with being scared to a certain point and there are still aspects of the ride that kind of creep me out.
One of the other reasons that I love it was because it was a time when Disney didn't shy away from the dark and grim. Just like making a ride about Pirates, Disneyland took something scary and of the occult and put their own fun little spin on it. You really don't see a lot of rides to that caliber anymore.
2) I would have to agree with another poster and go with the attic scene, it used to be one of the creepiest part of the ride for me. Now it's just laughable and more tongue-and-cheek then it is scary...