This movie has everything I love! SciFi, end of the world, character study... so many sociological implications! But it was missing one thing for me: an interesting story. If you enjoy slow moving movies with little or no conflict set in a post-apocalyptic world (are there many of those?) then you might enjoy this one.
IO refers to a moon of Jupiter where colonists fled to survive the Earth's decay. Humans have poisoned the atmosphere or maybe Earth fought against humanity. We're not really sure, but a generation or more ago, we started leaving the Earth because too many areas had become uninhabitable. The movie features a young woman scientist working with her father on trying to figure out the current sustainability of Earth. She gets a rare visitor who wants to take her to one of the last shuttles off of the planet. She is conflicted about whether she should stay behind to continue the work or leave and join with her boyfriend on Io.
Very little happens in this movie, to be honest. I have some theories about the movie that might be spoilers or ruin it for you, so I won't mention them here, but if you're interested, leave a comment asking "What are your theories?!!" and I will reply to it. I suppose you can ask other questions, too. I'll allow it.
Regardless, I didn't care for this movie. I didn't hate it. I just didn't really care about the characters or their outcome. It wasn't a person fighting for survival, but more curiosity or pride, even. Then another person comes along and he's not super sympathetic, either. I honestly would have rather had a movie about the colony on Io. I think THAT would have been fascinating! Plus, much of the science was WAY off, which always bothers me. So I didn't really care for the movie, but I didn't hate it. I liked Annihilation better, which is kind of a similar movie. Both are slow and character studies with some weird cinematic decisions in them. So I'd suggest watching that instead.