The captivating John Lydon is the best reason to see a documentary about Public Image Ltd. that tells you more about Lydon’s post-Sex Pistols band than you may want to know.

A good music documentary is more than a footnote to a band’s career — it can channel, and heighten, the excitement that made the band memorable. In that spirit, there is much to be said for “The Public Image Is Rotten,” which casts its eye back over the sprawling, tempestuous, gnarly, ever-mutating career of Public Image Ltd., the band that John Lydon put together just after the breakup of the Sex Pistols and that he has kept going, in one form or another, for close to 40 years. Having seen PiL in concert several times in the ’80s, I count myself as a modest fan.”The Public Image Is Rotten” is a solidly made niche documentary, one that can stand as a more or less definitive chronicle of a band that started off as an experimental art-rock curiosity and became, over time, a potently danceable and influential musical collective.

That said, there’s a slight forest-for-the-trees aspect to the movie. It is built, of course, around an extensive interview with John Lydon, who now resides in Los Angeles, and who talks to the camera sitting in his kitchen and drinking beer, his body thicker than it once was, his gleam of smiling misanthropy intact, his head shaved on both sides (for a hint of that punk-lobotomy aura). Lydon, who remains a sulfurously eloquent and charismatic figure, is open and ardent on the subject of PiL, but he’s fairly buttoned up about everything else — i.e., the state of the world. And truth to tell, it’s everything else that you most want to hear him sound off about.

There are tidbits in that direction. In “The Public Image Is Rotten,” Lydon looks back on the Sex Pistols with less disgruntlement than usual, discussing the death of Sid Vicious, his tossing off of the line “Ever get the feeling you’ve been cheated?,” and what it was like to go down to Jamaica, where he had become enamored of heavy-beat reggae, only to have Julien Temple’s cameras literally spy on him during the filming on “The Great Rock ‘n’ Roll Swindle.” “Johnny Rotten was a piece of work,” says Lydon, sounding about as close to nostalgic as he gets when he admits, “I wanted to be Johnny Rotten.” In clips from the time, where he looked like a bone-skinny, debauched Jesse Eisenberg, we see what he means: Lydon was actually quite serious and shy, and Johnny Rotten was performance art made real.

Lydon also discusses, with the humbled sincerity of someone who is now in his early 60s, the love and devotion he feels for his wife, the German publishing heiress Nora Forster (they’ve been a couple since the ’70s), and what it was like to have his memory completely erased at the age of seven, after a bout of meningitis that left him in a coma for three months. He emerged as a blank slate, filled with terror, not even remembering his parents (“You feel so guilty!” he says), and one can hear that echoed not just in the fear and loathing he expressed as Johnny Rotten but in his postmodern compulsion to view everything — including his own “public image” — as a sham.

Lydon would have kept calling himself “Johnny Rotten” but was barred from doing so; it was part of the legal tangle that left him broke, disgusted, and in a protracted war with Malcom McLaren. Public Image Ltd. was conceived to be his way out of the morass: a band that he alone would guide, and that would make its music outside the system. Their first song, “Public Image,” was a miracle of sound: astonishingly bright and propulsive, with scabrous lyrics but a highly original flow that was equal parts rock and glam and something else, all driven by a mad guitar jangle and the quickened majesty of Jah Wobble’s bass. The song excited people; it was proof that Lydon was no one-trick sneer. (The song was happy.) But the album didn’t live up to that title track — it was sparse, glum, and didactic.

And that mattered, since PiL, from the start, did everything but make money. As “The Public Image Is Rotten” rolls on, the squabbles and ego clashes that are part of the drama of any rock & roll band threaten to hijack the movie, because in PiL’s case those conflicts have more weight than the albums did. There are tales of Keith Levene’s substance abuse, and of how Wobble literally stole the group’s backing tracks to use on his own solo album. And before too long, the personnel changes start to pile up until you need a Flo-Chart to keep track of who’s in the band.

There are testimonials to how revolutionary PiL’s sound was from musicians like Flea (“It changed my life”), Moby, and Thurston Moore of Sonic Youth, who astutely hails the band’s second album, the fabled Metal Box, as “the White Album of the underground.” Moore was at the infamous Ritz show in New York — captured here with actual footage — in which the members of PiL played but refused to emerge from behind a movie screen, provoking such bottle-tossing rage on the part of the audience that the concert had to be shut down. Moore calls it one of the greatest shows he ever saw, but for some of us, that’s just the sort of story that captures why avant-rock can be so avant-dull. Refusing to face your audience isn’t a statement, it’s a stunt, and Public Image Ltd. — at least in my view — needed to shake off that leftover (bourgeois) anarchy to become a true band.

The grand irony of PiL’s career, which the movie could have played up more than it does, is that they became, for a time, a kind of deathless cerebral disco band, their career sustained by the downbeat propulsion of tracks like “This Is Not a Love Song” and “Rise.” It was during this period that Lydon truly found himself as a performer, bouncing around the stage like the rasta-braided psychotic court jester of the dance floor. He had found a way to touch the mainstream and not hate himself in the morning, a movement the film captures with clips of PiL’s music videos as well as the TV commercials that Lydon did for Country Life British Butter.

“The Public Image Is Rotten” is a documentary that serves its intended audience well. You might even call it an unofficial sequel to “The Filth and the Fury,” the great, lacerating, and majestic documentary about the Sex Pistols that Temple directed in 2000. Yet that movie told an epic story of the 20th century: how punk lived and died at the same moment. “The Public Image Is Rotten” unfurls a story that stretches on for decades, and the longer it lasts the smaller it seems. It’s John Lydon, far more than his band, who remains a grandly compelling figure: the icon of punk who was also punk’s assassin, and who lived to tell the tale.

Tribeca Film Review: ‘The Public Image Is Rotten’

Production

Director: Tabbert Fiiller. Camera (color, widescreen): Yamit Shimonovitz. Editor: Eric Pritchard.