A new documentary on actor and filmmaker Sylvester Stallone takes an odd but weirdly satisfying approach. Part career retrospective and part gushing hagiography, it would actually be mildly irritating were it not for the man himself: an accomplished talent with a wounded soul, and seemingly burdened by regret.

I must admit to being a keen fan of Stallone and his work. He is a genuine polymath of American cinema, demonstrating not only a distinctive acting talent but also evident skills in screenwriting and direction. His Rocky cycle of boxing dramas, that started in 1976 and extended to five sequels and three spin-offs, are a tremendous achievement in popular filmmaking. They also form the spine of the documentary. This makes sense: they tend to reflect Stallone’s own life in deliberate and unintended ways. Other key films get included and discussed in a linear manner.

Stallone’s life story is, in many ways, so stereotypical a “rags-to-riches” story that it risks feeling inauthentic. A forceps injury during birth gave him a lifelong facial paralysis. Ill-matched parents led to an unhappy childhood. Aspirations of acting professionally seemed futile until he wrote his own screenplay – then superstardom hit him overnight. From here a range of interview subjects – notably writer/director Quentin Tarantino and actor Arnold Schwarzenegger – enthuse about his wide-ranging creative talents. It is well-edited and paced, and attractively assembled, but it does seem to focus more on virtues than vices.

Thank goodness, then, for Stallone himself. He dominates the film through extensive interviews with its director, Thom Wimny. He seems a genuinely smart and thoughtful person. What is striking, however, is his humility and sadness. He knows of his own mistakes and shortfalls, and appears haunted by regret – particularly in scenes related to his son and father. Wimny seems to actively avoid any difficult subject matter, but his effort is repeatedly undercut by Stallone’s own melancholy. The film is framed by Stallone’s Los Angeles home being packed up by removalists before the man himself relocates east. Superficially it seems symbolic of a person looking back on their past, but in the light of Stallone’s apparent sadness it takes on a more melancholic dimension. All of the statues and art, the memorabilia and merchandise, fades into unimportance. There’s a tragic core here, about the relationships that were neglected and the ones that never stood a chance. It drags something more fascinating out into the open. It is subtle and fascinating.