Great ideas don’t always work.

Alexander Payne’s Downsizing was one of the most anticipated films of an already packed year. An original conceit debuting to early plaudits, if formidable, rendered too grandly here derails this otherwise entertaining flick.

Couple Matt Damon and Kristen Wiig, tired of, well, everything, take a chance on a new technology shrinking entire communities to a fraction of their size, thereby consuming less and allowing once six foot tall citizens to live in greater opulence.

The economic implications are but one dimension of a fascinating concept rife for social satire, with Payne and co cycling through a slate of consequences, some funny, some sad, some purely practical and others abundantly thought-provoking. Set, in the best traditions of science fiction, in a recognisably not too distant future, the first half of Downsizing offers tantalising insight into the limitations and frustrations of our own world by deploying a trope of cinema until now largely reserved for campy kids movies.

Christoph Waltz, as with almost any of his features, emerges a highlight, with Jason Sudeikis, Neil Patrick Harris and Laura Dern welcomely appearing in what are effectively cameos. Too overtly navigating the recent political upheavals in the United States in passing, Downsizing being only one of many green-lit projects inevitably catching up to the current reality, it is from this point that the film loses track in an extended, ill-judged third act.

Transporting Damon’s everyman from the comfortable boundaries of the premise’s satire into a world-changing, monumentally consequential series of events may wreak of the pointed societal entreaties Downsizing seeks to emulate, yet comes off more akin to the action extravaganzas where John Cusack et al somehow find themselves in the middle of something for which they are woefully under-qualified.

Cramming the lead into a hastily exposited jumble of moralistic sledgehammers may expound upon the filmmakers’ thematic intent yet too significantly detracts from what was otherwise an enjoyable and not infrequently mind-bending first half done little justice by the film’s regrettable conclusion.

Downsizing is in cinemas from Boxing Day