Fair warning: considerable spoilers follow – read after watching.

It is extremely rare to be surprised by a film. The way movies are written – especially those coming out of the Hollywood system – demands foreshadowing for almost every element of a story that might be considered surprising or might feel like it’s coming out of left-field. As a result, most big budget films are predictable. Look for the signs, and you can figure them out.

However, Downsizing is not one of those films. Directed by Alexander Payne, from a script by Payne and frequent collaborator Jim Taylor, Downsizing tells the story of the invention of a process that shrinks the human body to around 12 centimetres tall – a process the inventors conceive of as a way of reducing waste and helping save the planet in the face of a lack of resources, increasing pollution.

Payne makes the decision to follow Paul and Audrey Safranek (played by Matt Damon and Kristen Wiig), a couple who decide to go through with downsizing, but each for different reasons. However, their journey – and especially that of Paul – simply proves that, despite the obvious benefits, the baser instincts of humanity prevail. Instead of providing a solution to so many of the problems we face, our obsession with wealth and our tendency toward classism simply follow us into this smaller realm.

Downsizing is a film that is trying to say so many things about issues like global warming, about the human condition, about how we treat the less fortunate in our society – and it illustrates these points by taking the surprising route at every junction, from the early reveal (somewhat spoilt in trailers) that Paul’s wife backed out the last second, to the core “what do I do” conundrum at the end of the film, which I’m not going to spoil here.

In fact, I would go as far as to say that the final act features one of the most unpredictable twists that I’ve ever seen in a film of this magnitude. Downsizing seems to be heading in one direction, then all of a sudden it becomes about something else.

And that is the main problem with what Payne has put on the screen: when the narrative of the film is shifting so much, twisting in so many directions, it affects how hard-hitting your message becomes.

For example, through Paul’s interactions with Ngoc Lan (played by Golden Globe nominee Hong Chau), the film tries to illustrate how going small affects the poorest in society, and how societal hierarchies simply shrink along with us. But it loses impact because the next scene shifts so quickly into comedy, then into some other problem facing humanity.

Funnily enough, the scope of the film actually expands over the course of just over two hours, with each act bringing in more of the world, from an intimate focus on Paul Safranik, to a wider view of the small city of Leisureland, to a macro view of the world at large, encompassing all of humanity. But, as mentioned, the impact is lost as we leave the old points behind and move on to something else entirely.

Despite these narrative shortcomings, Downsizing is a pretty good film. Payne’s direction – building on the success of The Descendants and Nebraska – is minimal in style, allowing the actors leeway to play their characters more naturally, lending the proceedings a kind of authenticity. Chau and Christoph Waltz, in particular, deserve a lot of praise.

Damon does a pretty good job, I guess. I thought he was kind of hammy at times, and seemed to be a little confused by everything that is going on. But I can’t decide if that is a positive or a negative; Paul Safranik is meant to be a little pathetic, and meant to be in a little over his head. As a result, the character – and the actor – look a little lost.

I’m also a big fan of the production design. Payne wisely chooses to stick to what adds to the story he is telling, and avoids clichés – there are no giant rats running rampant through town, no scenes of people eating giant sandwiches for a laugh. When the size difference is used, it is used purely for either comedic effect (such as a nurse bringing a giant cracker to Paul) or to illustrate a point (such as the sheer wonder of giant butterflies visiting a village).

This is most apparent during an early scene that demonstrates the entire shrinking procedure from start to finish. The process is shown in such a way that it almost feels like a choreographed musical number, and is absolutely delightful – proving that when the film gets it right, it absolutely nails it.

Ultimately, though, the good can’t outweigh the shortcomings of the story here. An entertaining and surprising film it is, but I can’t help but feel a little disappointed that the writing wasn’t quite there to back up such an interesting concept.

Downsizing is written by Alexander Payne and Jim Taylor, directed by Payne, and stars Matt Damon, Kristen Wiig, Hong Chau, Christoph Waltz, Udo Kier, Jason Sudeikis and Rolf Lassgard. It is in cinemas now.