Shooting over two years and accorded exceptional access, debut documentary film-maker Alison Klayman has produced a tantalising and at times inspiring, but rarely penetrating, study of controversial Chinese artist Ai Weiwei. Part of the problem is that Ai is a master of self-promotion through his various artistic and social networking activities, which means he consistently sets the agenda, leaving Klayman merely to record rather than question or assess. His personal foibles go unchallenged here and no effort is made to gauge the quality of his work. Indeed, Ai is presented as something of a Warhol-like superstar, with an adoring entourage aiding him in the creation of conceptual pieces and the staging of political protests. However, there's no doubting his courage in challenging the government conspiracy of silence over the number of schoolchildren killed in the 2008 Sichuan earthquake, his denunciation of the Beijing Olympics or his pursuit of the policeman whose assault meant Ai needed emergency brain surgery. Fascinating, but frustrating.