French singer, songwriter and provocateur Serge Gainsbourg was never content doing things the way they were supposed to be done. During his career, he managed to set the sexual moans of two famous actresses to music, convinced a 16-year-old singer to record a thinly veiled paean to oral sex, and sang a duet with his own daughter about incest.

But setting aside his penchant for controversy, Gainsbourg’s musical influence remains gigantic, if only for his restless experimentation with genre and form. Comic artist-turned-filmmaker Joann Sfar attempts to similarly twist the conventions of the musical biopic — as well as court controversy by playing fast and loose with the facts — by following up his own graphic novel with a screen portrait called Gainsbourg: A Heroic Life. The resulting film is, at first glance, like no biopic you’ve seen before.

There’s a heavy dose of the fantastical in Sfar’s vision, nowhere more evident than in Gainsbourg’s “Mug,” an eerie, caricatured puppet version of the singer. First appearing as a gargantuan egg-shaped head with four arms and four legs, the figure steps out of an anti-Semitic propaganda poster to follow the young Gainsbourg (born Lucien Ginsburg) through the streets of World War II-era Paris. Later, the Mug reappears in the artist’s adult life, taking on a more sinister presence, with skeletal arachnoid fingers and a face dominated by a long beak of a nose and massive ears. It’s the most visible elements that comprise Gainsbourg’s self-described ugliness, made grotesque. And throughout the film, the Mug acts as the devil on the singer’s shoulder, providing advice with no angel to counter.

It’s that advice that leads Gainsbourg to abandon his early ambitions as a painter in favor of his father’s profession, music; when he embraces his musical talent as a means to an end larger than paying for art supplies, he’s quickly on his way to stardom, no matter how many personal relationships are sacrificed in the process.

Beyond the Mug and the other fantasy elements, though, Sfar’s film doesn’t color outside the lines as much as he might like us to think. Unlike another musical biography that used its form as an abstracted reflection on the character of its subject — Todd Haynes’ I’m Not There — Gainsbourg edges toward its goal without fully committing to the provocation its subject demands. Structurally, this is still a standard-issue chronological bio, with all the notes one would expect from an episode of VH1’s Behind the Music: the difficult childhood, discovery of an innate talent, a skyrocket ride to the heights of fame, a substance-abuse-influenced fall from grace and bit of atonement to wrap things up.

Sfar’s imaginative direction and the film’s lush visual sense, along with a hugely charismatic performance by Eric Elmosnino in the title role, do manage to elevate much of the formula elements. But the film suffers from the flaws that plague many a biopic that squeezes six decades of a real life into two hours; in trying to encompass too much, the portrait feels incomplete. Characters, wives, children often enter or depart the story unannounced. While that certainly reflects a solipsism on Gainsbourg’s part, the resulting narrative is still disjointed enough to grow tiresome, particularly when Sfar begins skipping even larger blocks of time toward the end of his subject’s life. Gainsbourg’s descent into drunken messiness isn’t quite glossed over — a risk with a film that so loudly proclaims its point of view in its title — but Sfar does rush through it, choosing to leave out some particularly notorious details, to find the redemptive place on the other side.

Of course he hasn’t pretended that Gainsbourg is meant to be an entirely accurate portrait, so strict adherence to facts isn’t entirely necessary. But what begins as an exciting exercise in experimentation has taken a turn into the mundane by the end. In another film, that could have been a sly statement on Gainsbourg’s own trajectory. In a film that treats him with as much reverence as this one does, it’s just a letdown.