This freewheeling, low-budget horror comedy suggests a millennial update of Brian De Palma’s 1970s work, as writer Simon Barrett and director Adam Wingard (You’re Next) turn a trashy genre exercise into a vehicle for social satire, ambitious camera work, and lots of movie parodies and homages. (The points of reference range from The Lady From Shanghai to Halloween to Gus Van Sant’s Elephant.) A small-town family receives a visit from a preternaturally calm young man (Dan Stevens) who claims to have served in the military alongside their late son. That’s a familiar setup, but Barrett and Wingard take it in one unexpected direction after another, displaying obvious pleasure in their mad dash to keep topping themselves. Be forewarned, though, that both the humor and the violence get progressively sicker as the story unfolds; chances are you’ll find this either hysterical or appalling.