“When you’re scared, what do you do?” asks the now-elderly Beach Boy Brian Wilson, a man whose mind conjures towering cityscapes of gorgeous pop noise but seems to struggle with its own silence. It’s an utterly sincere question, addressed not to the audience or to the air, but asked honestly of the interviewer; his friend, Rolling Stone’s Jason Fine. Brian is scared and genuinely wants help feeling better – a beat of intimate vulnerability rarely seen in traditional rock docs. It’s one of a handful of genuinely remarkable moments in The Long Promised Road, a documentary which, in some places, struggles to justify its existence in a crowded market of Beach Boy docs, but occasionally reaches compelling heights.

Like the Beatles, Stones and Who, the Beach Boys have an obsessively documented career, the band’s story is too intriguing, too era-defining and too twisty-turny to resist telling every couple of years, whether as fiction as in the excellent Love & Mercy, or in an endless stream of documentaries with greater or lesser results.

We know about the abusive, overbearing father who managed them, about the Surf-rock success that made them superstars, the drugs and excess, their masterpiece Pet Sounds, Brian reaching too high with his “teenage symphony to god” – the abandoned Smile album – and burning out, the mental health struggles, the over-eating, the controlling psychiatrist, the comeback. It’s a great story … just not an entirely fresh one. And compared to other Wilson documentaries, notably Don Was’s I Just Wasn’t Made For This Time and the fairly definitive film made when Wilson finally completed Smile as a solo artist in the mid-2000s, there’s much that The Long Promised Road doesn’t have.

For starters it doesn’t have many of Brian’s contemporaries – most of the talking heads are long-time admirers like Bruce Springsteen and Elton John, and comparative whippersnappers like Nick Jonas or Foo Fighters’ Taylor Hawkins. While Bruce and Elton are occasionally interesting on song composition, most of the guest interviews feel redundant. It’s also extremely light on the other Beach Boys (a quickly snatched few minutes with Al Jardine toward the start is all we get) and though Wilson talks lovingly about his late brothers, Carl and Dennis, Mike Love – not only alive but an important antagonist in Wilson’s story to this day – is barely mentioned, let alone featured. The furniture of the film and much of its well-trodden core story make the whole project feel unnecessary.

Brian Wilson – The Long Promised RoadWhere The Long Promise Road really flies is in the relationship between Wilson and Jason Fine, the editor of Rolling Stone who has been covering Brian’s work for decades and is now a close friend. Fine is as much a part of the film as Wilson – we seem him gently steering his subject to the right issues, and the trust between them yields beautiful moments. That “steering” is literally true, as well – much of the film features the pair driving around places from Brian’s life, talking frankly, playing old tunes, remembering. Wilson’s mental health issues are well documented – he has schizoaffective disorder, and still hears voices when he’s stressed – and his replies are often slow coming, the words being dredged up with apparent great effort. It’s difficult to watch, and it takes a close friend to know how to get the best out of him. Shots of Wilson at work in the studio are the only times we see him properly comfortable, in an environment he obviously understands instinctively. Here his whole demeaner changes; it’s the one place he seems to be in control of his world rather than confused by it.

The frankness with which Wilson and Fine talk yields some quite astonishingly candid moments – the point where Brian admits that he’s never heard his late brother Dennis’s classic album Pacific Ocean Blue, sitting in an armchair and hearing his little brother’s masterpiece for the first time in tears. The moment when Fine tells him that former Beach Boys manager and collaborator Jack Rieley has died, seeing Brian’s grief well-up in real time. It’s uncomfortable viewing but that’s not necessarily a bad thing in a film, and it’s rare that a documentary can get so close to the true soul of its subject.

It’s a film that switches between wonderful moments and pedestrian ones without ever finding a middle ground. Producer Don Was playing the unaccompanied vocals tracks for ‘God Only Knows’ is a staggeringly emotional experience, and few can be unmoved by the complexity and beauty of that heavenly arrangement. It makes you wonder why Nick Jonas’s opinion is worthy of our time when we could be hearing more of of Wilson’s undistilled genius.

There’s also some uncomfortable stuff – director Brent Wilson’s (no relation) decision to overlay a studio playback in which Brian looks uncomfortable with the voice of his abusive father seems at best a little on-the-nose, and at worse, given Wilson’s struggles with schizoaffective disorder, horribly inapropriate.