I don't have too much to say, except to echo the accolades that your other reviewers have given this masterpiece of suspense from France. The few people who found it too tame or dull are perhaps those enamoured of films with characters named "Jason" or "Freddy" !
Director Henri-Georges Clouzot's DIABOLIQUE is one of these movies we, in french speaking countries, have seen at least a dozen times on TV in our teen days. Always with pleasure. In part, because of the terrific cast but mainly because of the whodunit plot.
Based on the Pierre Boileau and Thomas Narcejac novel CELLE QUI N'ETAIT PLUS, Henri-Georges Clouzot's 1955 DIABOLIQUE is easily among the most influential films of world cinema, leaving its mark on everything from Alfred Hitchcock's VERTIGO and PSYCHO to William Castle's THE TINGLER--but even so, and while Hitchcock's masterpieces can be said to at least equal the Clouzot original, few if any of the films spawned by DIABOLIQUE ever bested it.