Recent evidence suggests that the Venice film festival likes to open big, with a bang or a splash, a movie to blow the doors off and reveal the cosmos in widescreen. Previous opening nights hurled the delegates from the black expanse of Gravity through the ensemble free-for-all of Birdman to the frozen wilds of Everest. But a tipping point has been reached; a corrective is called for. And sometimes it’s true that the best things come in small packages. Particularly when the package is as cram-packed with nourishment as Downsizing, Alexander Payne’s gorgeous, giddy parable of a modern-day Lilliput.

Matt Damon stars as Paul Safranek, an overstretched man in an overstretched world, working as an occupational therapist down at Omaha Steaks and still living in the house where he was born. Paul hungers for a fresh start and finds it courtesy of the newfangled technique of “cellular miniaturisation”, which promptly shrinks the recipient to a height of five inches. This technique has apparently been pioneered by scientists out in Norway, although one might just as easily claim that Payne has been doing it for years. Films like Election, Sideways and Nebraska, for instance, spotlighted a burgeoning crisis in American masculinity, focusing on men who fear that they’re seen as small by the world. With the excellent Downsizing, Payne has simply gone that extra mile.

The benefits for Paul are clear from the outset. As a little man, he costs less and consumes less. His assets of $152,000 convert to a whopping $12m in the bonsai community of Leisureland Estates, which means that he can now afford a McMansion or a luxury bachelor pad, like one of those cash-poor Londoners who sells their Hackney flat and then buys up half of Rotherham. A flick of the switch and the process is complete. Afterwards the nurses return to theatre and lift the clients from their beds aboard small steel spatulas.

Donwnsizing’s premise, then, couldn’t be more high-concept. But Payne runs with it, plays with it, explores its implications. Having ticked off the pros, he moves on to the cons. Miniaturisation, we learn, is prone to misuse: African dictators shrink rival ethnic groups; US Homeland Security is worried about pocket-sized terrorists infiltrating its borders. Meanwhile, out in Leisureland, Paul has befriended the rascally Dusan, his playboy upstairs neighbour, played with reliable zeal by the great Christoph Waltz. If this Eden has a serpent, it is undeniably Dusan, who is making a fortune smuggling in contraband goods. “It’s the wild west, baby!” he explains with a grin, reclining on his designer sofa during a brief break between parties.

The point, of course, is that glass-domed Leisureland is merely America in microcosm, with all the same corruption and wealth-disparity, loneliness and strife. Neither does it exist in splendid isolation. If the outside world starts to burn, then Leisureland is all-but guaranteed to go down in flames too.

What a spry, nuanced, winningly digressive movie this is. No sooner I had it pegged as a jaunty black comedy than it starts folding in elements of dystopian sci-fi, or compassionate human drama. A less polished director might have become lost and confused along the film’s lengthy running-time. But Payne’s handling is perfect. He never puts a foot wrong, rustling up a picture that is as bright as a button and as sharp as a tack. Downsizing contains multitudes. Inside, it’s a giant.