A good filmmaker knows when it’s time to leave his comfort zone, and Alexander Payne, four years after his last film, “Nebraska” (2013), must have figured that he’d taken the amblin’-road-movie-that’s-really-a-plunge-into-the-kooky-heart-of-Middle-America in about as many directions as he could. His new movie, “Downsizing,” opened the Venice film festival by unveiling a new side of Payne that’s at once playful, spectacular, mischievous and audacious. The movie, a comedy about groups of miniaturized humans who live in tiny villages (all to save an overpopulated planet), is an outrageously matter-of-fact science-fiction fairy tale — a kind of live-action Pixar movie on acid. It’s “Honey, I Shrunk the Adults” made by a deadpan social satirist.

It’s also the most whimsically outlandish film of Payne’s career, though that doesn’t mean it’s made with anything less than his usual highly thought-out and controlled master-craftsman bravura. “Downsizing” is an ingenious comedy of scale, a touching tale of a man whose problems grow bigger as he gets smaller, and an earnest environmental parable. It all adds up to a film that risks, at times, becoming a little too much, yet Payne, working from a script he co-wrote with his regular partner, Jim Taylor, has made that rare thing: a ticklish and resonant crowd-pleaser for grown-ups. The result should prove to be a major draw at the box office and a leading awards contender.

In the not-so-distant future, scientists at an institute in Norway perfect a process for reducing humans to tiny figures, about six inches tall, who can fit — and live — comfortably in an entire village of 7 by 11 meters. (Their disposable refuse for a year can be contained in a single ordinary-size garbage bag.) Payne, who has always been a poker-faced realist, knows that the most enticing way to treat this premise is with a restrained air of plausibility, as if it were really happening in our world. And so we see how downsizing gets turned into a marketing bonanza. It’s a radical way to cut down on the consumption of the earth’s resources, but the hook, for those who volunteer, is that they’ll live like suburban royalty.

Their assets are now worth 100 times what they were, and they’re invited to settle into sprawling McMansions and enjoy a life of endless hedonistic leisure. To become small is to become rich. The idea starts to look more and more appealing to Paul Safranek (Matt Damon), a mild-mannered occupational therapist who dresses in plaid shirts and Dockers and is still depressed over not having had the ambition to become a doctor. Paul’s wife, Audrey (Kristen Wiig), yearns to move into a bigger home, which they can’t afford, thanks to the bank’s income-to-mortgage-payment ratios. Payne touches the double nerve of our current economic jitters — the combination of shrinking paychecks and raw envy.

The audience, of course, knows in its bones that downsizing has to be a Faustian bargain. It’s sold by feel-good corporate gurus played by Neil Patrick Harris and a lolling-in-the-bathtub Laura Dern, who points out, to oohs and ahhhs, that the downsized can purchase a diamond bracelet for $83. Yet if there’s a catch to downsizing, it’s really right there on the surface: Who wants to be a dinky mascot version of him or herself? And there’s an additional catch: The process is irreversible.

That said, the temptation — of wealth, of the fulfillment of upscale dreams, with the added nudge of doing one’s bit for the planet — is strong. After talking to a downsizing counselor who sounds like she’s hawking theme-park condos, Paul and Audrey decide that they’re going to take the plunge. They will live large…by getting small.

Payne has a blast with the transformation sequence, a sinister procedure that involves having your fillings and body hair removed and then being lifted, nude and unconscious, by what look like giant spatulas. When Paul wakes up in his hospital bed, the nurse asks if he’d like a snack, and she produces a package of two giant Premium Saltine crackers — the hospital’s slightly ominous idea of a sick joke. (The food is, in fact, all appropriately sized.) But Paul, it turns out, has a much darker shock in store.

The most humane aspect of Alexander Payne’s movies is that he extends the hand of empathy to flawed heroes who are the most deeply ordinary of schlubs. In his greatest film, “Sideways” (2004), he and Paul Giamatti made that kind of character electrifying; in “Nebraska,” not so much. Matt Damon, in “Downsizing,” endows Paul with a passive sweet decency that makes him seem like a high-school dork all grown up (but essentially unchanged), and while Damon, as doughy as a Teddy bear, infuses the character with feeling, you may wish that Payne had given Paul a dimension or two beyond his lumpish decency and good nature — that he’d come with a few spiky quills. From the moment he gets to Leisure Land Estates, Paul is lost. (No one can even pronounce his last name.) “Downsizing” is the story of how he plugs back into his life — a journey of awakening enhanced by the film’s outsize comic curlicues.

Paul becomes friends with an obnoxious neighbor, played by Christoph Waltz as a smilingly self-satisfied Eurotrash entrepreneur who turns his apartment into a destination for druggy bacchanals. One aspect of downsizing, it seems, is becoming a suburban party animal. But there’s another side of the tracks, and it’s there that Paul gets to know Ngoc Lan (Hong Chau), a Vietnamese prison escapee who is missing a lower leg. They begin to heal each other, and Hong Chau’s performance is remarkable: She starts off as a borderline stereotype — a bitter refugee spitting venom in broken English — and then melts into the film’s most surprising character.

Payne may be the closest thing we have to a studio-system classicist. His films are built with a craftsmanship so beveled and honed that it’s beyond impeccable, yet that very precision can, at times, rob his movies of spontaneity. “Downsizing” has a subtly structured arc of redemption, as well as a nifty metaphorical design. It says that our obsession with having a “better life” can reduce us, and that life will always be a stranger journey than the one we thought we were choosing. But the movie, in the end, is more amusing than exhilarating, and what should be its emotional payoff hinges too much (for my taste) on the director’s apocalyptic vision of climate change. “Downsizing” turns into a movie about saving the human race. But it’s most fun when it’s about saving one man whose life turns out to be bigger than a hill of beans.