This is very definitely not a Hollywood movie - it's decidedly unglamorous, there are no dramatic action set pieces, there are no characters who overcome their failings to become heroes and save the day, the love story at the heart of the film is sad and awkward and very believable, and the ending leaves you with questions rather than closure. If you're looking for Passengers then this movie isn't for you. If you're up for a film that pushes you to think, that makes you examine the human condition, that asks you to work with it rather than just let it wash over you then give it a go.
The basic setup: at some point in the not-too-distant future, Earth's environment is collapsing. People leave the planet in huge numbers, ferried up into orbit by a space elevator and then transferred to shuttle craft the size of a small town that looks suspiciously like a shopping mall in Scandinavia (at first this is a bit jarring, but brings a level of mundane believability that is the film's hallmark). The trip to a new life on Mars is supposed to take just over three weeks, but shortly after the journey begins the shuttle - the Aniara of the title - has to change course to avoid disaster. It soon becomes clear that it will take a very long time to get back on track. Initially the passengers take solace in the emotionally reassuring virtual reality of the "Mima" room - a kind of recreational space where you can relive pleasant memories of Earth before the environmental collapse - but quickly this breaks down through overuse, leaving the passengers distraught. As the years stretch on the society on the Aniara begins to change, becoming more authoritarian, religious cults develop in response to the despair of the passengers and violence simmers. We follow this story through the central character of the "Mimarobe", the woman who runs the Mima VR room - just an ordinary worker on the ship, not a feisty heroine with unique abilities or technical skills, a regular person. Through her relationships with the rest of the passengers we feel the situation that is slowly unfolding, watching her adapt as things change.
Ultimately "Aniara" is about the loss of our world, the Earth that we live on, a meditation on the hubristic dream of thinking that we can replace this priceless planet with an artificial world of consumerism and luxury. The universe is vast and unreachable - we only have one home.