If you don't think too much about the science behind Downsizing, it's a pretty good movie. It's preachy, sure. But it doesn't just constantly beat your over the head with global warming warnings (but it's definitely mentioned several times). It's hard to compare this movie to others. It's strange and deep, yet approachable. It reminds me of something that might be an episode of Black Mirror. Delving into the 'what if' of technology.
Downsizing follows the story of Paul, who decides to 'go small'. His $150,000 from selling everything he and his wife own will be the equivalent of around $12 million in the world of the tiny. So they decide to go for it. Paul is the typical nice guy that sometimes struggles with the unfairness of the world. Still, he makes the best of every situation he faces, which makes him realistic, even if tragic at times.
I enjoy 'what if' movies. It was a bit hard to deal with a suspension of disbelief quite this big, but I think the movie handles it well. The movie shows that no matter what, there will be the haves and the have-nots. And some people are good, while others are bad, no matter where you are. Yes, it's pretty heavy-handed with the environmental issues, but it does try to pull back on it by the end with a mention that they might be a little more than crazy. In all, it's worth watching, even if you don't love it... I think you'll like it.