An emotional rollercoaster of a movie full of ethical dilemmas, Crash keeps you thoroughly engaged and constantly unbalanced as it follows a wide range of characters - black and white, Iranian and Korean, cops and criminals, rich and poor - through traumatic times. It starts with a carjacking, and writer-director Paul Haggis skilfully uses his characters to show how good people may do bad things and vice versa and how we all make assumptions based on appearance. While we routinely lambast Hollywood for its lack of ideas and brains, it would be churlish to complain that this has a few too many characters and dilemmas. It's nearly a terrific movie, let down a little by two whopping coincidences as pivotal characters meet up for a second time. This is particularly unlikely in LA, a big city where, as the film points out, everyone is kept apart from strangers because nobody walks.

Haggis, a TV regular who was Oscar-nominated for his Million Dollar Baby screenplay, explains on a commentary track shared with actor-producer Don Cheadle that the film sprang from his own carjacking in the 1990s. It's a far more atmospheric and unsettling take on a theme covered in Lawrence Kasdan's Grand Canyon, and includes a fine cast, many of them in unusually small roles. Ludacris, Cheadle, Thandie Newton and Matt Dillon acquit themselves particularly well, but the revelation here is Sandra Bullock, playing completely against type as a furious housewife and all-round Ms Uncongeniality with fierce conviction. It's a lightly flawed but mightily impressive directorial debut by the Canadian Haggis, maintaining that country's iconoclastic reputation.