Precious, Lee Daniels, 115 mins, (15)

The troubles of its central character are laid on with a trowel in a film that's part social tract, part dramatised talk-show therapy

Set in Harlem in the 1980s, the controversial new film Precious burdens its young African-American heroine with a world-class catalogue of woes.

Not only is Claireece "Precious" Jones extremely overweight, she's also friendless, insulted and violently abused at home, already the mother of a girl with Down's syndrome – whom she calls Mongo! – and pregnant for the second time at 16, by her own father. It gives a whole new meaning to the term "morbid obesity".

Based on a novel by Sapphire, Lee Daniels' film begins as a lurid, hard-times pantomime. Precious (Gabourey Sidibe) lives in a tenement apartment with her layabout mother Mary (played by comedian and chat-show host Mo'Nique). Early on, Mary throws a pot at her: falling to the floor, Precious instantly has a flashback of being raped by her father, with inserts of frying egg and sausage and Dad's sweaty chest. This nightmare is replaced by a screamingly-hued fantasy of herself resplendent at a movie premiere – until the dream is broken by Momma throwing water over her.

Mary makes Precious wait on her hand and foot, but occasionally forces on her an emetic diet of cold pigs' feet – apparently to keep the girl bulky, a slave to her own adipose gravity. There is no depth to which the monstrous Mary will not stoop – including speaking low and mock-solicitous as a preface to dashing Precious's baby to the ground. She has everything but the moustaches of a villain from Victorian melodrama, so that you almost expect her to hiss, "And never darken my door again, bitch!"

Then Precious is offered a place at an education centre, where she meets patient, compassionate teacher Blu Rain (even her classmates think this name pushes plausibility somewhat). As Blu, Paula Patton positively trembles with empathy and tender righteousness – at one point a single tear rolls down her cheek. Later, the same happens to a social worker played, with no-nonsense restraint, by a barely recognisable Mariah Carey.

Those tears clinched it for me. Usually, the most damning thing you can say about a film is that it's manipulative, but Daniels and screenwriter Geoffrey Fletcher have little use for such subtleties as manipulation. Precious simply tells us what to feel and when – horror, pity, joy, indignation. We constantly glimpse posters in the background: "I think I can", "Positive feeling is half of the work". In one scene, the walls of Precious's classroom come alive with exemplary scenes from US history. This is less a film than an animated brochure for self-esteem.

Well, that's laudable, and it would be good to think that Precious might change some lives for the better. To this end, Daniels deliberately uses the broadest strokes. At one point, Mary actually hurls a television at Precious and her newborn baby. And that's essentially what Daniels does to us, too – batters us with the shocks and big, easy emotions of daytime TV. It's no accident that Oprah Winfrey is on board as executive producer.

But the primary-colours crudeness is really most artfully contrived – after all, Daniels produced the extremely well-crafted Monster's Ball and The Woodsman, while his director of photography Andrew Dunn shot Gosford Park, for goodness sake. The film shows its hand as a knowing confection in the odd flash of sophisticated humour, as when Precious imagines herself into an Italian neo-realist film, with Mary as a caring Mamma proffering food: "Mangia, mangia, puttana!" (subtitle: "Eat, whore!"). And there's an outrageous self-reflexive touch when Blu asks her pupils to contemplate the sentence, "the author describes her protagonist's circumstances as unrelenting".

Apart from Patton's saintly Blu (you get compassion fatigue just looking at her), it's the acting that makes the film. Newcomer Gabourey Sidibe gives a tough performance in a part that mostly requires stoic impassivity, punctuated by cathartic bursts of exuberance. Sidibe carries the film and gives it dignity even at its most glaring extremes – and dignity is what the film is ultimately about. Mo'Nique gives the nightmarish Mary some considered modulation – there aren't many actors who could even conceive of delivering the line, "Your daddy died – he had that Aids virus", let alone with such face-value directness. And Precious's classmates work up a brisk sense of improvisational energy, especially Xosha Roquemore's trash-talking Joann.

Daniels has stated: "I did not make Precious for white America." And he certainly didn't make it for white middle-class English movie critics – so what I think may be academic. But I can't help agreeing with those African-American critics who – while many others have praised it as a breakthrough for black cinema – have seen the film as peddling grotesque, even racist stereotypes. Precious is part pamphlet, part dramatised talk-show therapy – and to be fair, it's honest about its intentions. But as cinema, it's just really bad, strident pulp.

Next Week:

Jonathan Romney sees Invictus, Clint Eastwood's film with Morgan Freeman as Nelson Mandela, and wonders: how much silver-haired gravitas can one critic handle?