Even with the unsettling setting (is it the '30s? the '70s?), the exaggerated head thrashing, the kinky Renaissance mistress-in-training start, and some lifeless dubbing, director Just Jaeckin's soft-core classic more than holds its own against today's mind-numbing, thrill-less ''adult'' cheesefests. A jarring dramatization of Pauline Reage's taboo-breaking 1954 novella about all-consuming obsession, pleasure, and pain, O is ripe for feminist outrage and psychoanalytical discourse, as its titular naif (Clery) endures repeated whippings and humiliation to prove her love and loyalty. But unlike most of the soft porn that followed it, the film leaves the brain with a little unexpected action of its own.