Jonathan Romney on Django Unchained: It's good, then it's bad. Well, it is Tarantino

You know you've started a controversy – a proper old-fashioned Straw Dogs-y hoo-hah – when your film is attacked by people who refuse to see it. That's the case with Quentin Tarantino's slavery-themed Western Django Unchained, which Spike Lee has boycotted on the grounds that it's disrespectful to black American history. But the other, more familiar controversy surrounding Django concerns its violence – a subject Tarantino seems to be weary of after all these years. Raise the topic with him, as Krishnan Guru-Murthy did on Channel 4, and you risk "getting your butt shut down" – to use a now-popular Quentinism. Few people – interviewers, producers or editors – have ever managed to shut down Tarantino's verbally effusive butt, and arguably the most excessive element of Django is neither the graphic depiction of slavery's abuses nor the copious bloodshed, but the endless blather.

Django Unchained is set two years before the Civil War, and its gunslinging hero is a freed black slave. But Django is less about American slavery than about the intersection of three movie genres: the spaghetti Western (notably Sergio Corbucci's Django, whose star Franco Nero has a cameo here); Seventies blaxploitation; and a somewhat disreputable cycle depicting slavery in a trashily erotic manner, eg 1975's Mandingo.

Tarantino's story begins with Django (Jamie Foxx), a slave on a chain gang, encountering a German dentist, Dr King Schultz (Christoph Waltz). Schultz is really a bounty hunter who wants Django's help in tracking down two bandits turned plantation overseers. In return, the affable Schultz proposes to school Django in his murderous trade. Cue the shamelessly anachronistic line: "Kill white folks and they pay you for it? What's not to like?"

Typically for Tarantino, Django is less an organic narrative than a series of routines, yoked together by a spurious mythic spin. Django's determination to free his beloved Broomhilda (Kerry Washington) leads Schultz to compare him to the Germanic hero Siegfried (has Tarantino been listening to Wagner, or just reading Hollywood's favorite dog-eared myth manual, The Hero With a Thousand Faces?).

The routines pile up, variously thrilling, beautifully executed and downright larky. Proto-KKK thugs complain that they can't see through their hoods. Django strides into action wearing ludicrous blue livery à la Lord Fauntleroy. A nerve-racking sequence focuses on a horrific slave-on-slave fight laid on to amuse poisonous fop Calvin Candie (Leonardo DiCaprio, silkily odious). And Robert Richardson photographs some magnificent scenery, from a rocky red desert to a wintry elk-filled prairie.

What really stops the show is Samuel L Jackson's outrageous turn as Stephen, Candie's ancient butler. It's Tarantino's most provocative move to create this nightmare Uncle Tom, an enthusiastic race traitor, and to play him for comedy. And it's a perverse, unsettling stroke to have this servile stereotype played, doddery whine and all, by the actor who in Pulp Fiction defined the contemporary cinematic icon of the Mean Mutha (another stereotype, but one whose chic tickled black and white viewers alike). It further twists the joke – and, you might argue, makes it acceptable – to reveal Stephen as not really subordinate, but the true power on Candie's estate. Many people will relish the joke – although I wonder how we'd have felt if Tarantino's war story Inglourious Basterds had included, among its comic-strip Nazis, an anti-Semitic Jew. This is not a frivolous comparison, given Tarantino's remark that he's out to depict "the Auschwitzian aspects of the slave trade in America".

Then there's the talk, as fountainous as ever. Tarantino's use of the word "nigger" is exorbitant even for him (Variety counted 109 instances), although given the antebellum setting, historical verisimilitude is on his side. But what's striking throughout is who does all the talking. At the start, Schultz mesmerisingly gabs through a scene leading to his dispatch of Django's oppressors. Then, with 100 rifles pointed at him, Schultz stakes all on his ability to disarm enemies with a silver tongue and the promise of gold (which suggests that he's a film-maker at heart: these two weapons are traditionally as effective in Hollywood as they are in Deadwood).

But while Schultz's rhetoric leads the action, Django himself is part action, part image, precious little language. Tarantino has claimed that he wanted "to give black American males a Western hero" – for which African Americans may well thank him, if they've forgotten roles played in the Seventies by Fred Williamson. But just as it apparently takes a white movie nerd to make a black screen hero these days, so Django himself is the creation of the urbane European who talks him into being.

It's only later that Django uses the linguistic wiles he's learnt. Till then, he's a man without a voice, oddly childlike. Among the film's black characters, only Stephen is granted any real discourse, while Broomhilda is pure apparition, a dream damsel glimmering tenderly at Django in his visions of reunion.

As usual with Tarantino, Django has style and invention aplenty, and as usual, some of it drags, doggedly reluctant to cut to the chase. But like Django in his blue velvet, the movie is a case of Tarantino dressing up in genre clothes, rather than getting inside the skin of the Western, as the Coens brilliantly did in True Grit. As for a righteous drama about avenging the injustices of slavery? More than any real engagement with the black experience, Django is about how white people love to talk, and how, once they start, their butts cannot be shut down.