Slumdog Millionaire, Danny Boyle, 120 mins, 15

This 'rags to rajah' story is pacily told, but the poverty and violence sit uneasily with splashy entertainment

(Film Still Imagenet)

Brio, zip, pizzazz, joie de vivre ... Danny Boyle's Slumdog Millionaire can't be faulted on any of these. Boyle has always been an energetic director, but in his new film he whips himself up to a state of euphoric intensity.

Set in modern Mumbai, Slumdog Millionaire is the picaresque story of a dreamer overcoming humble beginnings to make a fortune – rags to riches, or as one character puts it, "rags to rajah" – although the hero is less interested in the money than in long-fated love.

Based on Vikas Swarup's novel Q&A, Slumdog Millionaire follows the fortunes of Jamal and Salim, brothers from the Mumbai slums, whose saga begins with their mother being killed in a mob attack on Muslims. The two small boys take to the streets and team up with a young girl, Latika; they find shelter in an orphanage, only to learn that their benefactor runs a racket in beggar children, their bankability enhanced by mutilation. Salim, the tough counterpart to Jamal's gentle naïf, saves his brother from blinding, and the pair escape, living on their wits. A firm believer in destiny, Jamal dreams of finding Latika again, and eventually does – first as an adolescent, groomed for prostitution, later as a grown woman (Freida Pinto) and a gangster's mistress.

All this is narrated through an ingenious framing device. As a young man (Dev Patel, winningly candid and gangling), Jamal competes in the Indian edition of Who Wants To Be A Millionaire, and against all odds – he, a mere "chai-wallah" serving tea in a Mumbai call-centre – finds himself on the verge of winning 20 million rupees. We first meet Jamal while he's being questioned by police on suspicion of cheating – questioned, that is, with electrified crocodile clips on his feet. It emerges that every question Jamal answered on the show relates to an episode in his turbulent life.

Scripted by Simon Beaufoy, Slumdog Millionaire is smart and exuberant, and genuinely feels steeped in current Indian reality. It has an entirely Indian cast (apart from British-born lead Patel) and a primarily Indian crew (including casting director Loveleen Tandan, also credited as co-director), and it gives the impression of real awareness of the textures of Indian, specifically Mumbai, culture – notably the changes in the city, from slum vistas to the burgeoning skyscrapers of the new economy. The film feels a world apart from the just-visiting perspective of Wes Anderson's The Darjeeling Limited, which could barely bring itself to leave its luxury train compartment.

There's also a genuinely disturbing charge of realism in the depiction of the appalling slum conditions that the children grow up in, and the constant menace of severe violence. Effectively Oliver Twist redux, Indian-style, the film is certainly Dickensian in its constant shifts of register, in the way it asks us to take the rough with the smooth, the harshly realist with the sweetly fanciful.

Yet such polarities jar from the start: if you begin a film with a depiction of torture, you set a tone that makes it hard for the viewer to accept the shift into blithe wish-fulfilment.

On the one hand, we get a man set alight by rioters, a child's horrific blinding, the discovery of Latika in a brothel district. On the other hand, the film often seems most at ease in a mode of larky comedy: notably, in a brisk sequence of Jamal conning tourists at the Taj Mahal.

Perhaps it misses the point to complain about unevenness of tone when the film's raison d'être is that it aims for the all-inclusive scope of Bollywood films. But this isn't strictly a Bollywood pastiche: the element of social document is too hard-edged for that. The result for me was a distinct queasiness at being asked to accept genuine horror as part of a big splashy palette of entertainment. What most jarred was the scene in which seven-year-old Jamal (the very winning Ayush Mahesh Khedekar), desperate for the autograph of Bollywood megastar Amitabh Bachchan, drops into a cesspit and emerges plastered in shit. Maybe I'm just stuffy about poo jokes, but this worried me for several reasons: one, I'm not sure that extreme poverty and gross-out ribaldry make an effective match; two, it seemed an inadvertently depressing comment on what people, in India and elsewhere, will do in thrall to celebrity; three, dipping a small Indian boy in shit seems to me a dubious way of getting a laugh – even if the laugh is Jamal's.

Slumdog Millionaire wants to send us out with a smile, and eventually resolves into a tale of love triumphant, ending with razzle-dazzle credits and a Bollywood dance routine.

Well, Boyle set out to make this particular film rather than a gritty social panorama along the lines of Brazilian favela drama City of God. But keeping us cheerful takes the edge off the tougher insights into India, religious tensions included – and it's unfortunate that Mumbai now seems a less comfortable theme for a pop-melodrama blockbuster since the events of last November.

Besides, Boyle's feverish direction leaves us little space to appraise what we see. There's barely a shot that isn't a show-stopper – Boyle never tires of tilted angles and extreme close-ups, with director of photography Anthony Dod Mantle booting up the hot colours and staggering perspectives, and Bollywood master A R Rahman raising the pitch further with his lavish, buoyant score.

It actually comes as some relief, then, when we get into the quietly tense mode of Who Wants To Be A Millionaire?. These sequences are shot exactly in the internationally franchised style of the show, and Anil Kapoor – smoothly menacing in a glitter suit – makes a compelling host, creepier even than Chris Tarrant. You can't help suspecting outrageous product placement: Who Wants ... was created by TV company Celador, and the film is co-produced by its affiliate Celador Films.

Yet the programme actually comes across as an intensely sinister institution. And perhaps there's a suggestion of regret that in the Indian cultural imagination an impersonal piece of internationally-formatted product might be supplanting the homegrown glamour of Bollywood – that today, a Jamal might wade through shit to get the autograph of a Millionaire host rather than that of Amitabh Bachchan. But then, even big-screen demigod Bachchan did a stint as quizmaster on the show.