"August: Osage County" features a central twelve-person cast—easily one of the sturdiest ensembles of the year—and they all act their hearts out. Watching them navigate screenwriter Tracy Letts' spiky, cutting words, based on her Pulitzer Prize- and Tony Award-winning 2007 Broadway play, is close to spellbinding, enough so that one can mostly overlook the film's weaker areas. Although director John Wells (2010's "The Company Men") expands the scope by shooting on-location among the lived-in farmhouses, sweeping plains and dusty Main Streets of Oklahoma, this big-screen rendering is not always able to avert a certain staginess bred from the source material's origins. By slashing a nearly three-hour play down to two hours, some of the character beats also seem to be missing, while certain figures meant to play more emphatic roles—notably, dutiful Native American housekeeper Johnna (Misty Upham)—fall to the wayside as half-formed afterthoughts. A study in misery more than anything, "August: Osage County" is Bleak with a capital "B." Anyone who tries to call it a comedy must not be paying attention.

When Weston patriarch Beverly (Sam Shepard) goes missing, eldest daughter Barbara (Julia Roberts) heads back to her childhood hometown with husband Bill (Ewan McGregor) and mopey 14-year-old daughter Jean (Abigail Breslin) to give a little support to cancer-stricken mother Violet (Meryl Streep). Barbara's relationship with her mom has always been contentious, but, then, so has that of virtually every other family member circulating around Violet's truth-tellin' oxygen. When Beverly is found dead of an apparent suicide, the rest of the Weston clan convene for the funeral: responsible middle daughter Ivy (Julianne Nicholson), who stuck around after she grew up to tend to her parents; free-spirited youngest daughter Karen (Juliette Lewis), in from Florida with her latest handsome, lunk-headed beau, Steve (Dermot Mulroney); Violet's chattily controlling sister, Mattie Fae (Margo Martindale), and brother-in-law, Charlie (Chris Cooper); and Mattie Fae and Charlie's quiet son, Little Charles (Benedict Cumberbatch). What should be a time of harmonious reflection and remembrance goes downhill quickly, hang-ups from the past and dark family secrets threatening to boil over at any moment. For Barbara, whose marriage is dangerously on the rocks, she gradually begins to realize that as much as she cannot stand her mother, she is uncontrollably turning into her.

The play's the thing, but the actors in "August: Osage County" are far more than merely players. Tracy Letts' script is verbose—there are clearly a bunch of monologues and spoken setting establishments (like talk of it being hot) meant for live theatre—but the performers dig into these complicated people and appear to be relishing the opportunity. There may not be quite enough interactions between some of the characters, but what is there paints an aching picture of the bonds that unite family members and the bad blood that can tear them apart. Meryl Streep (2012's "Hope Springs") and Julia Roberts (2012's "Mirror Mirror") head up a superlative roundabout of thespians, neither one in it to be liked but both essaying flawed individuals with whom they obviously understand and find sympathy. Streep's work is, per usual, uniformly exceptional and vanity-free; her Violet is ill and has seen better days, but she keeps coming at her daughters and relatives like a freight train that doesn't know when to stop at the station. Wreaking havoc through her over-medicating ways and seeming inability to censor herself, Violet is the kind of woman, late into middle age, who is angry at what life has dealt her and dead-set on causing chaos and guilt in those around her. As oldest daughter Barbara, who got away (but not far enough), Roberts turns in one of her very best dramatic performances. As she ages, she is becoming less the radiant ingénue and more of a layered character actor; if that is the direction she wishes to take her career, the potential is already within her.

The rest of the ensemble add welcome color and depth to their Middle American milieu. Julianne Nicholson (2004's "Little Black Book") is quietly yearnful as Ivy, for the first time in her life ready to leave the nest and start living for herself—if, that is, she gets the courage to openly come clean about being in love with first cousin Little Charles. As the talkative, naive Karen, Juliette Lewis (2010's "Conviction") begins as the movie's version of comic relief before bringing underlying pathos to a sad, multilayered woman nearing forty who has relied on far too many unreliable guys during her lifetime and has never let herself properly grow up. Margo Martindale (2013's "Beautiful Creatures") and Chris Cooper (2013's "The Company You Keep") are nothing alike as married couple Mattie Fae and Charlie, and this is exactly why they are so plausible as spouses. Martindale's Mattie Fae is a big personality who likes things her way, while Cooper's Charlie stands back from the crowd, resolute but on the edge of finally speaking his piece. His father-son bond with an against-type Benedict Cumberbatch (2013's "12 Years a Slave"), poignant as the sensitive, withdrawn Little Charles, is beautiful, if undernourished. All the same, one scene they share where Cooper tells his grown child he loves him is breathtaking. Rounding out the top-tier cast are Abigail Breslin (2013's "The Call"), as the rebellious, vintage movie-loving Jean; Ewan McGregor (2012's "The Impossible"), as Barbara's fed-up, unfaithful husband, Bill; Dermot Mulroney (2013's "Stoker"), as Karen's flashy but questionable fiancé, Steve, and Sam Shepard (2013's "Out of the Furnace"), making the most of his brief appearance as the troubled Beverly. Misty Upham (2012's "Django Unchained") is positioned at the onset as the eyes and ears of the audience—the outside looking in—but so very little is done with her that she blends into the background until right near the end.

"August: Osage County" is almost entirely without resolution, and this proves to be its curse just as much as Letts' and Wells' point. Oftentimes, there is no true closure between family when a falling-out occurs, and certain relationships are destined to not quite mend themselves. By the concluding scenes of the film, possibly irreparable damage has been done to these lives, and the lack of hope leaves one both unsettled and not wholly satisfied. Beyond the terminal dysfunction of these people, what is there, really, to say? "August: Osage County" wallows in their unhappiness, and in place of a light at the end of the tunnel is more darkness. This is an uncomfortable, downbeat drama, humor deriving from pain and the rest rather straight-faced and grim. The performances are worth the experience, more so than a story that doesn't deliver the amount of insight or enlightenment it thinks.