In “August: Osage County,” we enter the story (based on the Tracy Letts play), of the appalling Westons who live in Oklahoma. The disappearance of the patriarch, a poet and a drunk (Sam Sheppard), brings together the members of this spectacularly dysfunctional family. In the stifling heat, they claw and tear each other to pieces, they cuss, yell, and throw at one another’s face awful revelation after awful revelation.

Intelligent writing and great ensemble acting make “August” fascinating. As the monstrous mother Violet Weston (Meryl Streep at her bitchiest) dominates, perhaps too much as she tends to when not held on a tight-enough leash. Spectacular as she is, she is occasionally overshadowed by her daughters: Barbara (brilliantly played by a violent, harsh, foul-mouthed and altogether remarkable Julia Roberts—who knew?), Karen, with her ditzy patter, not to be distracted by reality (Juliette Lewis, who makes us regret not seeing her more often), and Ivy, quiet and introspective in her losing battle for the right to have a life (Julianne Nicholson, who makes us regret not knowing her more.)

John Wells gives much room to the women, not least Margo Martindale, Abigail Breslin and Misty Upham, and less to the men, except for Chris Cooper. Still, every cast member is in top form as their characters unfold without ever falling into carton cutout or becoming predictable. Everyone in that family is gasping for survival, caught in their genes and longings as the past is revisited, old stories aired and festering wounds reopened.

We sweat and swear and hurt with all of them and mostly we cringe. There is not one comfortable moment in the entire two hours, it’s all dysfunction piled upon dysfunction. “August” makes us realize how essential minimal social consensus is necessary in our dealings with one another. Existing barriers of language and emotion are there for a reason. Cross them and life becomes impossible, as this powerful film demonstrates.