I had never heard of "Suspiria" or Italian director Dario Argento until about a year ago when someone (I think it was Luciaphil) brought up this movie, which included Joan Bennett's last screen appearance.
I had mixed feelings about the movie after seeing it on the SciFi channel at that time. I've come to conclude, though, that that airing didn't provide a good basis for evaluating the film. The color was washed out, both the print and sound were terrible, and the film seemed to have been chopped to bits for television. I was intrigued enough from from this suspect airing, though, in addition to reading a lot of commentary, to purchase the VHS tape, which was a revelation in comparison. (Incidentally, it is also available on DVD in restored format, as is the VHS version.) I also learned that "Suspiria" was the first in a proposed trilogy conceived by Argento, and that the second part had been filmed, "Inferno." In fact, I rather prefer "Inferno" to Suspiria ... it has the same stylized, unrealistic quality both visually and in terms of the storyline. "Inferno" is one of the movies where I think virtually every frame exactly fulfills the director's vision for the movie. And with Inferno, the implication is made more clearly that we are entering the realm of the subconscious, and that events unfold with no more logic than a dream or nightmare.
Argento's inspiration for the trilogy came from English writer Thomas de Quincy's dreamlike meditations in his autobiograpical "Confessions of an Opium Eater", in which he imagines three "mothers" -- spirits or shades, if I remember correctly -- who inspire and inflect mankind in equal measures. The link is rather tenuous, IMO, based on my reading of the relevant sections in de Quincy, but interesting.
For years (decades, now) there's been speculation as to when, if ever, the final installment of the trilogy would ever be undertaken.
The good news is that Argento has told a number of European publications that the third movie is in the works and he expects filming to commence in August. The working title is "La Terza Madre" (The Third Mother), and he says it will deal with gnosticism (a Christian offshoot -- heresy, really -- that I've always been deeply drawn to) and persecution. The movie centers on Mater Lachrymorum (Latin for "mother of tears"), whom he imagines as the most cruel of the three "mothers"; we will first see her in medieval Rome. Witchcraft will also play a role. Now, I'm not expecting anything like a realistic depiction of gnosticism, but as a backdrop to the third movie it sounds interesting.
A final note: Argento has said on the record that he originally conceived of the school in "Suspiria" as a school for little girls -- not the young women it turned out to be. The movie would probably have been even more horrible that way, and I wonder if it might have been better, too.
Also -- from what I remember, I don't think Joan Bennett considered this movie to have been high art ... I think she brought the right qualities to her role as the school mistress, however.