AS high concepts go, this finger-wagging sci-fi-tinged social satire from writer-director Alexander Payne certainly grabs the attention: what if we all lived small?

Things start in a Norwegian lab where scientists have discovered a way to shrink human beings down to a fraction of their size. Thus begins a 200-year-long plan to “downsize” the population as perhaps the ultimate answer to the world’s environmental problems.

One of the major incentives for people to choose to undergo this drastic, irreversible transition is that money goes a long way down there. This attracts financially strapped married couple Paul and Audrey Safranek (Matt Damon and Kristen Wiig) who decide to go for it as a way to escape their humdrum existence and live like kings in the world’s premiere small community known as Leisureland. Soon after arriving, however, Paul finds that miniature life isn’t all it was promised.

The film starts out fairly well, immediately compelling with an oddball premise chalk full of potential.But what starts out as an intriguing idea swerves into an unexpected, unwelcome and irreparably clunky territory. Considering Payne has given us such wonderfully astute society-under-a-microscope character studies in everything from Sideways and About Schmidt to The Descendants and Nebraska, it’s bizarre and disappointing that the film which actually shrinks its characters down to microscopic size is so tonally uneven, narratively scattershot and far too thematically heavy-handed.

On paper its messages about apathy towards climate change and how greed seems to prevail over empathy are admirable and worth exploring. But they are most effective in the strict confines of the shrinking concept, the drama only really working when focusing on what it means to be reduced and how life can be lived that way.

But it switches gears when Paul meets Ngoc Lan Tran (Hong Chau, giving a fantastic performance in a caricature of a role), a Vietnamese refugee who has lost a leg as a result of her punishment-by-downsizing, now trapped working as a cleaner for seedy luxury goods importer Dusan (Christoph Waltz), sure to be one of the year’s most irritating characters.

By that point it’s travelled over the line from admirably principled to full-on preachy as it hurtles towards a bizarrely apocalyptic final act. Ironically it loses the power of its messages precisely because it feels the need to so heavily ram it down our throats. It all adds up to a disappointing misfire with big things on its mind but ultimately little to say.