Undoubtedly the best film Dario Argento ever directed, Suspiria remains one of the most artistically pleasing films I've ever seen, horror or otherwise. From the incredible sets and magnificently vivid use of color to the morbid and influential soundtrack (think Einsturzende Nuebauten or Controlled Bleeding way, way before those bands existed), there simply is no other movie that looks or sounds the way Suspiria does.
Set in Germany, the story revolves around a young student who enrolls at a prestigious dance school only to find that there are some very weird goings-on happening there. There is murder, mayhem, and mystery, always a good combo, and it's pulled off very well.
Upon it's release in 1977, the film was both lauded for it's artistic vision and genuinely scary moments and panned for it's remarkably complex and detailed death scenes that were viewed as both ultra-violent and misogynistic.
Argento's previous films had been much more rooted in the Italian Giallo style of mystery and Suspiria was his first legitimate "horror film". The movie is, supposedly, the first in a trilogy entitled the "Three Mothers" about three separate witches, all related through some common thread that is set to be fully explained in the upcoming film The Third Mother. The film was shot with anamorphic lenses allowing for incredible wide screen shots, particularly towards the film's finale. The lighting is deliberately vivid and overblown, creating a surreal and creepy look in nearly every scene, though none more so than where the students are set to sleep in the school's gymnasium. As the lights go out, the entire screen is bathed in dark red light and the tension becomes taunt based only on that simple trick. Amazing.
Being 30 years old, the film's special effects hold up remarkably well, though this is probably due more to the strength of the overall production than any technological wizardry. It's ability to scare comes not from any sudden surprises, but the ever present feeling of dread and tension. It is an incredible film that should be required viewing for any horror fan.