Imagine that, at the age of eleven, you had starred in a motion picture, that in years since has been widely acclaimed and derided as one of the worst pictures ever put to film. This is the most important thing that you have ever done; so much so, in fact, that at the age of 28, you decide to direct a documentary about the film, and its significant cult following. You do this out of a sense of both pride and nostalgia, and your documentary is a celebration, a laid-back and entirely happy look at how a certain kind of movie fan has taken up this wretched gobbet of cinematic flotsam as an iconic kitsch masterpiece, and given some real meaning to the most important thing you have ever done. And you did it at the age of eleven.

Let that soak in a bit, and you'll start to understand both the casual, easygoing appeal of Best Worst Movie, and the delicacy of its depiction of broken but indefatigable humans. Michael Paul Stephenson's concise but loving tribute to the making of the inexplicably godawful 1990 horror-fantasy Troll 2, in which he played the lead role, is at once a silly bit of fluff and something deeper and sadder: a chance for several bad movie icons to take stock of what they have done in their lives, and determine whether their one claim to a limited and dubious fame has been worthwhile to them or not. Read close enough in between the lines, and you'll find a movie that, with tremendous gentleness, cuts to the very heart of the human desire to make a mark on the world.

Stephenson's journey into the world of Troll 2 fandom began with another ex-star of that film, George Hardy, who played Stephenson's dad. A practicing dentist when he took the part, and a practicing dentist still, Hardy appears in the film as one of those preternaturally smiling folks, who doesn't seem to possess the ability to feel pessimism. The first moments of Best Worst Movie find him recalling his initial viewing of Troll 2, in which he realised to his terror that he was an unfathomably bad actor who would be forever tarnished by his relationship with this piece of crap; even as he giggles and laughs while telling the story, you can't help but feel that he giggled in 1990, watching himself made the clown of the world.

Hardy, genial and up for adventure, is the film's protagonist, if that's the word: Stephenson's camera follows the dentist from massive sell-out shows in New York, Boston, Chicago,** Seattle, where he reconnects with old co-stars and the film's director, Claudio Fragasso, and finds that he is a celebrity; to horror conventions and a hometown fundraising screening, where he finds that he isn't. You can spot the exact second, practically, in which Hardy goes from being "man, I'm such a beloved bad movie star, I should do this forever" to "man, I miss being a dentist in Alabama", and the aftershock of that moment is not one of soul-wracking doubt, but of simple, pragmatic understanding. Sort of an, "oh, this was fun, but it's time to wake up now", and Hardy's indomitable energy makes that realisation quick and painless.

Though he is the focus of the documentary (owing, no doubt, to the huge kick he got out of riding along with Stephenson for the whole experience), Hardy's grand arc only expresses in longer form what the director finds true of all their co-stars: Connie Young (Troll 2's daughter) candidly but without rancor acknowledges that the film has cost her parts; Robert Ormsby (the grandfather) acknowledges that, at the end of his life, he's done virtually nothing of lasting use, but at least he got to star in a famously bad movie (which he claims, and I believe him, was always one of his life goals). Some of the participants' stories are sad: Don Packard confesses to being so doped-up and clinically insane during the shoot, that he doesn't remember. Some are terrifying: Margo Prey, caring for a sickly mother for God knows how long, has retreated into what can only be called a fantasy world. Mostly, though, they smack of amusement: the recognition that one's obituary will begin with a reference to something this pointless mingled with the awareness that one will be mourned by thousands of people.

Besides Hardy, Stephenson's favorite subject is Fragasso, whose insanely arrogant defenses of the film are the comic highlight of the movie. He doesn't make films for the critics, he claims - and it's very easy to believe him. He patiently explains why Troll 2 is a masterpiece of social observation: and from the co-writer and uncredited co-director of the execrable Hell of the Living Dead, that's not an unreasonable claim to make (that's the grimmest truth about Troll 2: it's absolutely not the worst film in Fragasso's career). And yet, when this cocksure Italian ass comes face to face with the crowds who find his ineptitude hilarious, it's almost touching to see the pain flickering on his face. Damn you, Michael Paul Stevenson: you made me feel a little sorry for Claudio Fragasso.

Along the way, the film touches on the many people who've seen and loved Troll 2, explaining why they love it; and a better defense of the necessity of bad movies I've never seen, even if I can't follow as far as the folks who earnestly claim that it's not actually "bad", that it's not to be loved ironically. That might be true for Showgirls, it sure as hell ain't true for Troll 2. But I digress: though it spends little time focusing on the audience in favor of the actors, Stephenson still has enough love left over for the only people who'll ever regard him as an important movie star to devote a good portion of Best Worst Movie to celebrating the fans: paying tribute to the communality that comes from surrounding yourself with other cult movie lovers and making fun of a bad movie as one. There really is nothing at all like it: the feeling of being surrounded by fellow fanboys or cinephiles at a superhero movie or film festival hasn't got a patch on it. I do not know that any film has ever tried to depict this weird sense of unity before Best Worst Movie; I am convinced that none has done it so well.

It's not art; it doesn't try to re-imagine what documentary filmmaking can look like; Best Worst Movie is just really nice and really fun. It's a human story, not a making-of documentary - if you've never seen Troll 2, there's little lost, especially since the most relevant scenes are shown at the appropriate moments - but it's such a touching human story, so filled with so much affection for everyone who wanders onscreen, that it's hard not to respond to it warmly. It really is a tribute to human endurance: most of the people we spend time with ended up somewhere far different than they wanted to, but most of them are pretty content, and none of them have given up. Pretty strong stuff for a film about something as resolutely worthless as Troll 2, but that's the thing: all those bad movies were made by real people with beating hearts, and that's part of what makes us love them.