The most famous image in ET is Eliott and his alien seated on a flying bicycle, silhouetted against a bright full moon. A change in Steven Spielberg's outlook is evident in AI, where the moon has transformed from an emblem of wonder to a cosmic threat - as though heaven itself is intent on destroying the protagonist's dream of happiness. Taking inspiration from Brian Aldiss's short story "Super-Toys Last All Summer Long" and following a detailed treatment by the late Stanley Kubrick, AI is the first movie of Spielberg's career that doesn't aspire to mass acceptance. In a distant future vanquished by ecological disaster, a childlike android named David (brilliantly portrayed by Haley Joel Osment) is the first prototype afforded the ability to love. But when that love is no longer needed, he embarks on an Oedipal quest for meaning amidst a human population so terrified of being replaced by androids that android-lynching has become a public entertainment. AI comprises three distinct movements representing, in sequence, birth, life and death. David's pursuit of love is entirely selfish, but (in Kubrickian belief) it is self-fulfillment that propels all human action. David's cause cannot be dismissed on the grounds that he's mechanical, because his capacity to love means he's been unethically supplied with a conscientious sense of purpose. This is challenging, painful science fiction, caught among Greek tragedy, religious parable, Pinocchio and the robot novels of Isaac Asimov. It frustrates and provokes - beginning with the universal moment of a child asking his mother if she'll ever die, and launching through the darker, more isolating recesses of a boy's imagination. Spielberg prolongs the film for 20 minutes after an ample denouement presents itself. Though what follows is tonally perplexing, it's a fascinating coda, bringing David's adventure full-circle while launching concepts about the evolving state of machinery - as well as those explored in 2001 - to a different philosophical galaxy. There are images and ideas in AI that I can't get out of my head. Even when it's infuriating, it's the most densely layered science fiction film in years: a visionary bedtime story for adults.