It’s difficult, indeed impossible, not to be moved by the story of Solomon Northrup, a free black man in New York who was kidnapped by slave traders and, after twelve years in bondage in Louisiana between 1841 and 1853, finally liberated, going on to write a memoir of his horrendous experience that appeared almost simultaneously with “Uncle Tom’s Cabin” and was briefly almost as widely read. “12 Years a Slave,” adapted (with some streamlining and simplification) by screenwriter John Ridley and director Steve McQueen from that book, certainly depicts the inhumane treatment Northrup suffered under even the most enlightened of his “masters” (not to mention the purely sadistic ones), and for that reason alone it’s a significant contribution to an art form that has generally tiptoed around the nation’s original sin up until now.

But McQueen dilutes the visceral impact of the story by too often succumbing to the artiness and visual affectation that so strongly characterized the style of his two earlier pictures, “Hunger” and “Shame.” As a result his film is an important work, but one that’s more potent on an intellectual level than an emotional one. It might be argued that the distancing of McQueen’s approach mirrors the somewhat anomalous situation of his subject. Northrup, after all, was different from most of his fellow slaves in that he had known an America where, though his civil rights were circumscribed by his color, at least he was not treated as property. As portrayed by Chiwetel Ejiofor with exceptional nuance, Solomon is introduced, after a brief prologue showing him working in a sugar cane field, as a musician in Saratoga Springs, where he lives comfortably with his wife and two young daughters. Enticed to Washington D.C. by two fast-talking men with an offer of well-paying employment, he’s wined and dined, only to find himself in a dismal cell the next morning, shackled and charged as a fugitive slave ready for transport “back” to the south. (McQueen demonstrates his penchant for visual emphasis—or overemphasis—at the end of this sequence by pulling the camera up from the courtyard in which Northrup must bathe to show the Capitol as the immediate background of his mistreatment.)

Northrup is then shipped, along with others similarly snatched, to New Orleans, where a slave trader ironically named Freeman (Paul Giamatti) sells him to plantation owner William Ford (Benedict Cumberbatch). The sequence is enlivened by Giamatti’s tense, flamboyant performance, and given extra punch by the anguish of another slave, Eliza (Adepero Oduye), who’s separated from her children, who are sold separately. That begins the more benign stage of Northrup’s—or Platt’s, as he’s been renamed—ordeal. Ford proves a relatively decent owner, a man conflicted about the societal system he’s part of but afraid to rebel against, and willing to embrace—and use—his slave’s expertise in the lumber business. Such moderation, however, is no part of the character of Ford’s chief carpenter John Tibeats (Paul Dano, once again doing his maniacal shtick perfectly), a vicious racist who enjoys humiliating Platt until the slave turns on him, to be saved from death only by Ford’s intervention. The closing sequence of this chapter, in which Northrup hangs suspended from a tree while the other slaves go about their business seemingly oblivious to his plight, is another of McQueen’s artful touches, perhaps intended as a rebuke to the famous long crane shot of the burning of Atlanta in “Gone With the Wind,” only one picture whose romanticized portrait of Dixie “12 Years” is designed to demolish.

Ford thereupon transfers ownership of Platt to Edwin Epps (Michael Fassbender), a steely-eyed psychotic whose affair with sensual slave Patsey (Lupita Nyong’o) leads his jealous wife (Sarah Paulson) to egg her husband on to ever greater cruelties. McQueen uses Epps to represent the depths of depravity in the supposedly genteel southern racist culture, depicting him brutalizing slaves for failing to pick enough cotton each day and not only beating Patsey nearly to death when she displeases him but forcing Platt to participate in the gruesome act—a long scene that will force many viewers to avert their eyes. Ultimately it’s only the intervention of an abolitionist-minded Canadian carpenter named Samuel Bass (Brad Pitt), to whom Northrup confides his history and who informs the man’s New York friends of his situation, that secures Northrup’s release and tearful reunion with his family.

There’s so much that’s superb in “12 Years a Slave”—the intense performances by Ejiofor and Fassbender, an astonishingly vivid turn by Nyong’o, and stellar work from Giamatti, Cumberbatch, Dano and Paulson—that its failings are all the more regrettable. In addition to McQueen’s tendency to choose an arty visual alternative too often—perhaps encouraged by the almost painterly images fashioned by cinematographer Sean Bobbitt—there are lapses toward the close that suggest that both the director and Ridley were running dry. That’s unfortunately most evident in the scenes featuring Pitt, who also served as one of the producers. Bass’s pronouncements are the only elements in the film that come across as preachy, largely because Pitt’s delivery lacks the concentration and urgency that might make them seem like firmly-held convictions rather than words on a page. The final scenes of Epps’s fury over being denuded of his property and Solomon’s return to his family right matters, but the damage lingers. As was the case with Steven Spielberg’s “Lincoln,” McQueen’s film is impeccable in its period detail, with the production design (Adam Stockhausen), costumes (Patricia Norris), art direction (David Stein) and set decoration (Alice Baker) all estimable.

McQueen’s film, in fact, invites comparison to Spielberg, not only in terms of “Lincoln” (which, after all, dealt with slavery more indirectly), but “Schindler’s List,” which dealt with another of the most barbarous realities of human history and also ended in a victory that seems very small in relation to the horrors that surrounded it. “12 Years a Slave” will be termed by many the best film about slavery in the United States that’s ever been made, but that has little meaning, as there have been so few of them, and those there are not terribly good. One’s appreciation of it is muted, however, by the realization that it could have been better still.