Matt Damon sci-fi comedy 'Downsizing' is a small wonder

Here's a fun game to play at the movies. Before you take your seat for the new Matt Damon sci-fi comedy "Downsizing", take a guess at where you think the movie will end up. The closest guess wins a free dinner or a million bucks or whatever -- the prize doesn't matter because neither you nor your buddies will guess anywhere near what actually happens.

"Downsizing" is a new sci-fi comedy written and directed by Alexander Payne, the man behind such heartfelt, low-key treats as "Sideways" and "The Descendants". It begins with an exciting breakthrough in technology as scientists discover a way to shrink people down to 5-inches tall, which of course shrinks their carbon footprint and their impact on the environment at the same time.

Payne engagingly explores this technology and the new world it creates, and then... well, just kind of keeps going. What starts off feeling like a lighter episode of "Black Mirror" heads off on an unexpected and very lengthy tangent.

Matt Damon stars as Paul Safranek, a schlubby everyman from a quiet corner of Omaha. Struggling with money and frustrated aspirations, he and his wife, played by Kristen Wiig, come around to the idea of being shrunk down to miniature size. When you're a few inches tall, a dollar buys a lot more -- even a multiple-room mansion or a diamond necklace are affordable when they're teeny-tiny. And so we head for the miniaturised town of LeisureLand, an idyllic community of tiny people in tiny houses under a protective bubble (to keep out insects).

Payne hilariously puts the the shrinking process and shrunken world under the microscope. The cheerfully surreal first half of the film is packed with sight gags and lovely comic detail, like a regular-sized clip-on lapel microphone becoming a huge mic for a shrunken scientist, or full-sized nurses carefully spooning newly-miniaturised little people onto tiny stretchers with special spatulas.

But obviously things don't go to plan for our mini heroes, who soon find the problem with starting a new life is you bring your old problems right along with you.

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Payne's fictional solution to environmental problems slyly suggests people will only make positive changes if there's something in it for them. And the film examines the idea that we all live in a bubble, comfortably unchallenging of our prejudices and blissfully ignorant of the wider world's problems. Yes, it does this by literally putting the characters in an actual bubble, but it's realised with such charm and so many great gags that we'll forgive how on the nose it is.

Once miniaturised, Damon's character finally begins to see the invisible lines that divide society, noticing the haves and have nots for the first time. As well as covering the environment, the mini metaphor allows the film to touch on health care, migration, consumerism, globalisation and other hot topics. 

Interesting as this is, the film kind of starts again half-way through. Clocking in at 135 minutes, you could practically split "Downsizing" into two movies, so disjointed is the second half from the first.

Wiig and Jason Sudeikis are both prominently featured in the first part of the film only to shrink from view in the second, leaving us with just Damon's amiable loser to carry on. The problem is he's deliberately boring, an example of the small-minded small fry who would benefit from enlarging their horizons. Fortunately Christoph Waltz and Hong Chau turn up to provide some big laughs in the small world, but having spent so long on the setup the spiralling second half soon outstays its welcome. The laughs dry up for something more worthy before tipping over into frankly baffling, setting up an ending you almost certainly won't see coming. 

"Downsizing" opens in Australia and the US in December, and the UK in January. It certainly has big ambitions, even if the wandering story could do with being cut down to size.

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