While Amy Scott's documentary is stronger on admiration than analysis, it gives a good sense of Ashby's achievements and his unusually attractive personality. Interviews with surviving colleagues, such as his mentor Norman Jewison, leave no doubt about his capacity to inspire love: not all respected filmmakers get spoken about in such fond tones.

Rounding out the picture are tape recordings of the man himself, along with enthusiastic tributes from a younger generation of filmmakers including David O. Russell, Alexander Payne and Judd Apatow, suggesting Ashby's influence endures even if he's no longer anything close to a household name.

Thankfully, the film isn't wall-to-wall praise. While "peace and love" was Ashby's mantra, he struggled to put this philosophy into practice in his private life – or so we're told by his daughter Leigh McManus, who barely knew her father growing up.

Also acknowledged to a point are Ashby's addiction issues, even if we're left to speculate on how far these factored into his career downturn in the 1980s (his lesser-known films from this period get relatively short shrift here, though some critics have defended them in the past).

Ashby's drug of choice, we're told, was marijuana, supplemented by cocaine from the mid-1970s on. But accounts of his obsessive work habits even in earlier years, not to mention his tendency not to sleep for more than two hours at a time, may leave you wondering whether we're getting the full story.

If you have even a casual interest in 1970s American cinema, Hal is worth an hour-and-a-half of your attention – especially for the archival material it contains, much of which you're unlikely to come across elsewhere.

In my personal pantheon, I have to admit, Ashby ranks nowhere near as high as, say, John Cassavetes or Robert Altman. But in his mix of sweetness and stubborn resistance to authority, he's not the worst role model for filmmakers today.