Last House on the left from Imdb:
"Much as I admire it, I can only watch Wes Craven's brilliant debut feature once every few years; as sheer stomach-churning brutality goes, it makes SALO look like Sondheim. Craven has said he made the movie as extreme as it is as his comment on the obscenity of Vietnam. I've heard that number many a time (Ruggero Deodato blames CANNIBAL HOLOCAUST on the Red Brigade!), but in Craven's case, it's so palpable it's believable. LAST HOUSE may be the first (and is certainly the most far-out) case of a horror movie that eschews suspense, tingles, shock, in the wake of sheer, harrowing barbarism.
Based on Bergman's THE VIRGIN SPRING, it tells the tale of a couple of young girls on their way to a concert who fall prey to a Manson-like family. Their rape-murders are avenged by a suddenly wised-up couple of parents who, in their restitution, find themselves as blood-bespattered and guilty as their prey.
LAST HOUSE ON THE LEFT is a grindhouse GUERNICA, an outcry over desensitization to violence that leaves you feeling shaken and desolated. It genuinely reupholsters the word "horror." For most, the clarity of Craven's intentions won't be enough to redeem the dire viciousness of what the director puts you through. For me, the ferocity of the movie has a cleansing, Artaudian pureness.
One question: Craven made this film and his masterpiece, THE HILLS HAVE EYES, the ultimate statement on the nuclear family in post-Woodstock, post-Altamont America. He then went on to make a load of occasionally mildly amusing but mostly godawful movies. What's the story?"