Kristen Wiig, Matt Damon in 'Downsizing'
CNN  — 

“Downsizing” is a bit too big for its britches – a movie that wrestles with several provocative themes, then seemingly draws back from them to pursue more conventional ones. Director Alexander Payne ultimately brings it all around to a fairly satisfying place, but that’s after a perplexing journey that’s at times more surreal than Gulliver’s adventures in Lilliput.

At its core, or at least start, the movie hinges on a science-fiction premise steeped in environmentalism, as well as an old Steve Martin routine: A program to shrink people down to just a few inches tall, dramatically reducing their footprint on the planet, and thus potentially making Earth’s resources go that much farther.

A big part of the pitch to “Get small” is an economic one, tapping into yearning for the good life and uneasiness about financial prospects. That’s what wins over Paul (Matt Damon) and his wife Audrey (Kristen Wiig), a fairly ordinary couple who are shown a time-share-like presentation that promises they can move into a dollhouse-sized mansion for a fraction of what it costs to live in middle-class suburbia.

The buy-in, however, means relocating to a community of the similarly small, one shielded from unique outside concerns, like, well, hungry birds.

Paul’s plans take several unexpected turns, and expose him to a whole new group of people. They include his free-spirited, libertine neighbor Dusan (Christoph Waltz, who gives the whole movie a welcome shot of adrenaline) and the former Vietnamese dissident Ngoc Lan Tran (Hong Chau, who arrives late in the movie and winds up largely stealing the film when Waltz isn’t).

At first, it’s all pretty amusing, even thought provoking, beginning with the fact that the scientific process at work originated in Norway, which makes the tiny accessories feel like one ongoing joke about Ikea-like Scandinavian efficiency. Damon also buries his movie-star attributes as a simple guy willing to take a sizable risk to find a scientifically provided version of the American dream.

Still, Payne and co-writer Jim Taylor pile on enough odd, bordering-on-arbitrary twists that they wind up occasionally losing contact with what the film was initially about. After having gone to great lengths to explain its premise, “Downsizing” thus shifts gears about halfway through, becoming a pretty good movie, just not exactly the one you’d been watching until then.

Payne certainly has a knack for quirkiness and eccentricity, attributes that served him well in films like “Election” and “Sideways.” Yet while “Downsizing” exhibits similar qualities and tone, the second-half developments make it difficult to stay fully invested in the film.

Ultimately, Payne brings it all back to a fairly basic rumination about what’s really important in life and assessing priorities, in a way that’s filled with warmth, sweetness and even a sized-to-scale ray of hope. It’s just that in order to get there “Downsizing” trades in the bigger, more ambitious movie it initially promises to be for what feels like a considerably smaller one.

“Downsizing” opens Dec. 22 in the U.S. It’s rated R.