Watching Slumdog Millionaire is like being run over by a carnival. It is a colourful way to go, if you don't mind being cut short in your prime. But you cannot help thinking that back then – in your prime (an hour or a minute ago) – you were enjoying plain life and reality, while there is none of either in Danny Boyle's feelgood Mumbai tale. It explodes like a street festival, from the early scenes of scampering poverty and tragedy, filmed like demented out-takes from City of God, to the 20m rupee climax on an Indian television version of Who Wants to Be a Millionaire?, whose previous questions, pinning the hero Jamal (Dev Patel) to his spotlit dreamtime, have been spaced through this multiple-flashback movie to structure and punctuate it.

Visually Boyle is on Trainspotting form, full of heady inventiveness. He deserved a script that matched his stylishness. But screenwriter Simon Full Monty Beaufoy, adapting Vikas Swarup's novel Q & A, has springcleaned it of credibility and substituted what could charitably be called a fairy tale. The point about a fairy tale, though, is that it has one far-fetched premise – the ignition key to its story – after which everything purrs logically from point to point. Here every scene is a wild whimsy, lashing the viewer on through wonder, joy, tears and every other strenuous, ersatz caprice in its weather system.

Each moment makes its point like a party piece, then passes on. The spirit of aspiration bursting up through poverty? That will be the scene of the pre-teen Jamal (Ayush Mahesh Khedekar, pictured above) staggering forth from a latrine-dunking to hustle a passing Bollywood superstar for his autograph. Love? That would be Latika, Jamal's childhood girlfriend, who grows up through three different performers until reaching the flower of womanly beauty (Freida Pinto). Ruthless Mumbai corruption? That would be the snarling pimp who enslaves her and also the cops who, startlingly, drag Jamal away from Millionaire's first recording session and torture – yes, torture – him to determine if he was cheating.