While Downsizing is ultimately a masterclass in how to squander an awesome concept, its first twenty minutes or so are actually really great, even if they do set up an interesting movie that, in the end, never really happens.
At the heart of the film is an irreversible process called downsizing, which involves shrinking people down to a few centimetres tall in order to combat global warming and overpopulation. Paul Safranek and his wife Audrey eventually decide to "go small" themselves, with all the benefits of downsizing (good for the environment, financial gain) proving difficult to resist.
At this stage, Downsizing seems intent on telling a story about Paul and Audrey's married life within the downsized community, but in an unbelievably cruel twist, Paul undergoes the procedure only to discover that Audrey has backed out at the last minute, and will not be joining him.
This was a genuinely shocking turn because it was clear that Audrey really did love Paul, but the fear of leaving her family and friends simply got the better of her. By leaving Paul on his own, the twist made you feel deeply sorry for him, a smart decision by the writers because it gave viewers a firm emotional connection to the downsized world, which, otherwise, may have felt too silly and distant.
In the end though, Downsizing threw all of that good work away by going with a random and nonsensical end-of-the-world plot instead. It was like the writers paid their kids to finish the script off.