When we first noticed him, he was a coltish, spikey-haired singer in wedged shoes and makeup, fielding questions from a talk-show host about his sexuality. When last seen he was a mature, married man, a slim and elegant figure in a suit, topped with a modish hat. Where did all that come from in the first place, and whatever was it that happened along the way?

Moonage Daydream takes its title from the Bowie hit of the same name that was released 50 years ago. It doesn't try to address the question of who was David Bowie exactly, so much as offer a kaleidoscopic experience of the images and sound that make up the Bowie experience. If, like me, you have not been a particular fan of his music or attended a Bowie concert surrounded by ecstatic male and female fans, this may be the next best thing.

Man/woman/robot? What was he? Even from outside the orbit of fandom, he was hard to ignore. With hindsight, we can see that when he adopted his Ziggy Stardust persona early in the 1970s he was among the first of the gender-bending pop stars to celebrate transgression.

He has consistently escaped definition of any kind and this sprawling, rhapsodic documentary written by Brett Morgan is not going to change this. Let the opening credit to a "cinematic experience" be your guide.

It's at least revealing that the somewhat dumbed-down persona Bowie first offered the public is different from what we see of Bowie in his articulate and thoughtful presence in middle age, when he talks about his painting. He wasn't bad with a brush in his portraits of people, often Turkish people in Germany, who were separated from their families.

Themes of solitude and loneliness dominate all of his creative output, as Bowie himself acknowledges in the occasional voiceover. There were many family secrets and an "incredibly" ordinary childhood, but at the same time a positive, warm relationship with a half-brother who introduced him to Kerouac and Coltrane. One of the consequences of resisting fate and never becoming the person he felt he was destined to be was a sense of being adrift.

At the same time, he felt he had to put himself through everything, to tough out unpleasant new experiences, and had a determination to never waste a day on this journey.

He tried on many personas as a performer, and as an actor too. He was a convincing fit as the extra-terrestrial who just couldn't find his way home in Nicolas Roeg's The Man Who Fell to Earth. We hear he was the first pop star to play a lead role on Broadway, the lead in The Elephant Man. And in Nagisa Oshima's WWII prison camp drama Merry Christmas, Mr Lawrence, he brought a hint of sexual ambiguity to his titular British officer.

It wasn't that Bowie was a particularly good actor. It was that his presence on screen could be compelling, with or without makeup or props.

The restlessness, the refusal to be categorised and the drive to find new language for his artistic voice, defined his career. As Bowie said, he used his face and body as a canvas. Some of the philosophising sounds pretentious, at least this remarkable performer of diverse talents had a rationale for continuous reinvention. And he sought a new authenticity in later years.

Some recurring images in this Morgan documentary are taken from Bowie's travels in Asia. As a tall, pale, androgynous man he attracts stares wherever he goes. He was always out of place, always adrift.

There isn't much that's new here on a star about whom there are already significant numbers of books and films, all attempts in their way to define and pin down this elusive celebrity. All in all, it's experiential rather than informative, and it's likely the man himself would not have had it in any other way.