It’s hard to say if the excoriating debut film written, produced, and directed by Fran Kranz, in being an extraordinarily depressing chamber piece dealing with the long-after fallout of a school shooting, is the last film we should have expected from the wacky “Dollhouse,” and “Cabin in the Woods” alum, or exactly the film he was always going to make, setting out his stall as a filmmaker of serious intent, to be taken seriously. Whatever the case, it is highly effective, and his talent undeniable, even if it does sometimes seem like it’s a talent for dragging nails screeching down your psychological chalkboard, or for torturously slow emotional band-aid removal. “Mass” features several of the strongest performances you’ll see this year (including an extremely welcome big-screen return for Martha Plimpton), and directorial confidence and cleverness that makes what’s largely a one-room, four-way conversation feel cinematic despite its deliberate claustrophobia. But there is also something ever so slightly suspect in its remorselessness: it makes you feel – my God, does it make you feel – but it’s possible to emerge, shattered, at the other end not quite sure why, or what do with all that feeling.