There were many questions swirling around the announcement of a Robbie Williams biopic as a key player in the fall festival season. For many Americans, the question might be, well, who is that? And for those who do know him, the question might be, well, who is that for? While the lives of musicians might have become easy IP for lazy film-makers and indulgent stars, there’s still nothing particularly unique about the life of Williams and certainly no urgent need to tell it at this very moment. And why would it then be costing a reported $110m, attract Paramount as backers and the Greatest Showman director Michael Gracey, landing an in-demand Telluride festival premiere?

Then, as people finally got to see it in the mountains, these questions received an answer no one was expecting because that answer was: monkey. Rather than going down the overly trodden traditional music biopic route, Better Man features a CGI monkey in the lead role, a film then made equal parts Rocketman and Planet of the Apes. From afar, it sounded like an intensely annoying gimmick, perhaps fitting for an entertainer who can often be intensely annoying himself, but the film, which moved from Telluride to Toronto for its second major festival slot, is a surprising winner, a reason to cheer in a subgenre that usually makes us want to boo.

Using top-end, hyper-expressionate motion-capture technology, actor Jonno Davies plays Williams as he goes from a working-class background in Stoke to becoming part of the boy band Take That to splintering off to find success as a solo singer, all narrated by the singer himself. Williams was a born showman, a quality his neglectful father (Steve Pemberton) took credit for, and became quickly aware that it wasn’t always talent that propelled but sheer confidence. Gracey, and first-time co-writers Oliver Cole and Simon Gleeson, take us speedily through his life but the unusual casting choice, and some bombastic set pieces (including a dazzling Regents Street Rock DJ parade), quickly ensure that this is no normal bullet point biopic.

Gracey’s involving and immersive direction sweeps us up and out of our seats, refreshing beats that have grown musty in this territory (does every musician have a bad dad and a drug problem?) with endlessly inventive transitions and montages that find ways to offer something unexpected. It’s not only Gracey’s electric style and the central gimmick that make Better Man feel like an upgrade, it’s the disarming honesty of Williams and how he’s allowed himself to be portrayed. Biopics involving their subjects tend to be eye-rollingly flattering, cowardly ignoring anything that might put them in a negative light. While Williams has always had a caddish frankness about his foibles, it’s still quite surprising just how much, in a genre that usually fawns, he’s willing to admit. We see him as a shitty boyfriend, a thoughtless son, a terrible friend and an unpleasant person to work with (he refers to himself as a “fucking twat”) and the film doesn’t easily explain it all away as the result of childhood trauma and/or his excessive cocaine habit (the film has more coke than a season of Industry). Unlike this year’s so-so Amy Winehouse biopic Back to Black, Better Man doesn’t shy away from the sweaty, smelly unpleasantness of addiction and unlike that film, it also doesn’t ignore how viperous the singer’s father could be (like the Winehouse biopic though, it does give a wonderful Mike Leigh actor – this time Alison Steadman – the chance to play nan).

Ir’s a shame given how affecting and tough the father-son scenes become that the film then gives his father a bit of an unearned victory lap at the end at a point when I was hoping for something a little less pat and celebratory, finishing it all on a bit of a bum note. There’s also a mischievous underplay of the importance and genuinely good pop songs that came during Robbie’s time in Take That (Sean Baker’s recent Palme d’Or winner Anora offers a more deserving and entirely unexpected tribute to one of their songs). The focus is understandably more on his solo music, not a greatest hits album I was ever hoping to hear again, in all honesty, but his songs are well-scattered by Gracey who emphasises their grand theatricality, as if they were always intended for a musical.

Better Man is a fascinatingly tough proposition for a wider audience and I’m still not quite sure how it will go down, how it will be marketed and who exactly it might be for. It’s a big-budget, big-emotion musical filled with hard R-rated swears (the word cunt is used liberally), nudity and extreme drug use as well as specific UK pop culture references (Nicole Appleton! Heat magazine! Top of the Pops!) – even if it wasn’t led by a monkey, it’d make for a challenge. It’s a film that exists on the precipice of falling apart but you’ll be surprised how well it stays together.

• Better Man is screening at the Toronto film festival and will be released in UK cinemas on 26 December and in the US on 17 January