The new documentary 'Sleep' by Natalie Johns is about what many consider Max Richter's magnum opus - an eight-and-a-half-hour composition 'Sleep' with 204 movements in a plangent, ambient and mellow vein, designed to be listened to while the audience is asleep. This new docu focuses on an open-air event in the Grand Park in Los Angeles. Guardian's Peter Bradshaw says the docu on "this toweringly quixotic work" is a "beguiling film" and "anything but a snooze".