It's difficult to underestimate the significance of The Clash in rock 'n' roll. They belong on any serious list of the top five rock 'n' roll performers of all time, and their 1979 masterpiece London Calling belongs on any list of the top five albums. But beyond that, do we know who they were? Julien Temple's new documentary Joe Strummer: The Future Is Unwritten attempts to answer that question, although if you want to know more about Mick Jones, Topper Headon or Paul Simonon, it'll have to wait for another movie. This is Strummer's world, and we all just wish we were living in it. The movie begins, like any biography, with Strummer's parents. His father was a diplomat that moved from country to country; Strummer was born in Turkey as John Graham Mellor, and later insisted on being called "Woody" before adopting his legendary moniker.

The singer, songwriter and guitarist attended art school, lived as a squatter in an abandoned London flat and busked on the street before forming his first band, a rockabilly unit. But when he saw the Sex Pistols play, he decided to move in a different direction. The Clash was born, and with it a series of extraordinary shows and five great albums. But only the movie's first hour is dedicated to the Clash. As Strummer intones on the soundtrack, they made every conceivable mistake: success went to their heads, too many drugs, etc. They even made up a few new ones. The band grew successful, they began squabbling and they lost their direction. Temple includes a terrific sequence in which he intercuts two performances of "White Riot," one from a small club in 1977 and one from a giant stadium in 1983, brilliantly illustrating how big they grew and how far they fell.

The film then turns to Strummer's years following the Clash, including a brief and ill-fated new lineup (who recorded the infamous 1985 album Cut the Crap that no one, not even Clash fans, will stoop to owning). He worked on a few movie soundtracks, notably Alex Cox's underrated Walker (1987), and appeared in Jim Jarmusch's Mystery Train (1989). He recorded a solo album, Earthquake Weather, which may have been just a way to get out of his long-standing contract with Epic Records. But mostly he sulked and brooded, sometimes spending time with his daughters, and other times disappearing into the desert. He toured with the Pogues, but it wasn't until he formed the Mescaleros in the late 1990s that he began to find a new kind of happiness. He suddenly admitted to being a hippie, and enjoyed talking to people and discovering new kinds of music. Temple peppers the movie with excerpts from his BBC radio show, "Joe Strummer's London Calling," in which he celebrated his favorite music, including, yes, Elvis Presley. Strummer died just before Christmas, in 2002, just after sending out a handmade Christmas card.

It's a great story arc, and this alone makes the movie worth seeing, but Temple's filmmaking may frustrate more than it enlightens. As with his 2000 Sex Pistols documentary The Filth and the Fury, he has a fascination for using talking heads, but obscuring or denying any information about them. He doesn't use identifying titles, and doesn't even care if anyone's face is lit. So we have an endless parade of bandmates, girlfriends, musicians, friends, producers, etc. with absolutely no idea who any of them are. A few big-time movie stars and easily identifiable celebrities turn up, such as Bono, Flea, John Cusack, Johnny Depp, Steve Buscemi, Matt Dillon, Martin Scorsese and Jim Jarmusch. And it's not too hard to eventually guess which talking head belongs to Mick Jones, but the rest is a blur. Moreover, Temple insists on filming everyone sitting around campfires -- something Strummer enjoyed during his final years -- and though it's an interesting visual trick (it's better than the standard studio interviews), it also comes across as a little precious.

As for the archive material, Temple has amassed a great collection of Clash performance footage, though it's mostly chopped up; we rarely hear an entire song all the way through. And when it comes to Strummer's youth, Temple uses clips from old TV shows and movies (including the animated film Animal Farm, Peter Cushing in an old BBC TV production of 1984, and Malcolm McDowell in Lindsey Anderson's if...) to illustrate life in the boarding school and in the abandoned flats. This technique feels cutesy at best and dishonest at worst. Since we don't get a good look at Strummer's face until much later in the film, viewers may be wondering which of the black-and-white schoolboys in this old film stock is actually him.

Temple is a veteran music video director, having shot things like ABC's "Poison Arrow," Culture Club's "Do You Really Want to Hurt Me?" and David Bowie's "Blue Jean," and his feature films almost always have something to do with pop music, yet he has never figured out how to move past a short attention span. He's constantly worried that we'll lose interest, even in a story as ferocious and passionate as Joe Strummer's. Certainly the movie could have been worse; it could have been directed as one of those ultra-bland PBS jobs, but Temple's vision takes it too far in the wrong direction. I suspect that Scorsese, who briefly worked with the Clash on The King of Comedy (1983), would be the guy to make the true Strummer film.