There is nothing negative I have to say about this movie. I love the soundtrack by Italian prog-rock band Goblin. They also worked with Argento on his director's cut of Romero's Day of the Dead which I also highly recommend. Goblin, with some assistance from Argento, create an atmosphere that sounds like Lucifer himself is at the mic. It never lets up in its relentless creepiness and is brilliantly done.
The architecture used in this film is also strange and effective. The set decoration is impeccable and the organic curved lines of doors and wall paintings make the mansion where the story takes place feel like its alive.
The acting is also very good with Jessica Harper [Shock Treatment, Minority Report] playing American ballet dancer Suzy Bannion who has come to study dance at a prestigious German ballet school. I also love the over the top Nazi wanna-be dance instructor Miss Tanner, played brilliantly by Alida Valli. She adds a great deal to the overall feel of the film.
As a disclaimer, Suspiria is not for the faint of heart. It's one intense movie that grabs the viewer by the throat and never lets you go. However, even if this kind of movie is not your cup of tea, it's hard to deny the brilliance of Argent's direction and artistic vision for Suspiria. I don't think there's another film out there quite like it.
For more info check out the film's entry in IMDB.