I’m Still Here purports to be a fly-on-the-wall peek at the life of Joaquin Phoenix following his self-imposed exile from acting and his supposedly pending rebirth as a rap star. If that were the case, the film would be little more than a claustrophobic, occasionally troubling—but ultimately unremarkable—portrait of a struggling artist. Thankfully, however, this is a film you can’t trust.

Early in the film, a hooded Phoenix declares that he “don’t wanna play the part of Joaquin anymore,” before ramblingly questioning the existence of his “real” personality. This question, verbalised so pointedly at the start of the film, is an obvious nod at the film’s wilful reputation as nothing more than a calculated media-stunt passing itself off as serious film. To dwell on this distinction, however, is to miss the point. It is precisely the tension between fact and fiction that gives the film its thrust, the accusation of hoax eventually serving as the launch pad for the star’s dramatic decline into Howard Hughes territory.

I’m Still Here certainly isn’t perfect (the handful of celebrity cameos—Ben Stiller, P. Diddy amongst them—feel particularly staged), but it is legitimately inventive. Affleck (making his directorial debut) supplies enough moments of real emotional resonance to make the film worthwhile (Joaquin’s arrival for the infamous Letterman appearance in particular is chilling—a limo door opening into a cascade of boos, shutter snaps and cold-white flashes wielded by a mob throbbing with palpable hostility). Ultimately, the film’s “truth” is immaterial. By dragging us through a real-life-yet-staged performance, I’m Still Here succeeds in opening a new perspective on society’s obsession with celebrity that would be impossible to achieve through pure documentary reportage or staged drama alone.

I’m Still Here opens in cinemas in Melbourne September 16.