Another interesting part of the story is the tropes it combines. The most prominent being the classic tale of Man vs. Nature. This kind of story is elevated in an interesting way by setting it on a foreign planet instead of on Earth. It's a survivalist story, but instead of being about a man fighting a bear, or a hurricane, or freezing snow, it's about an astronaut. The story of a marooned man often takes place on a mountain or a island, so putting it in the not-so-distant future, on a not-so-distance planet is a genius way to revive the genre and make it interesting.
It's out in the same category as other space operas, such as 'Star Wars', 'Mass Effect', and 'Firefly' though I'm not sure I'd call 'The Martain' a space opera like those other stories. According to wiki, a Space Opera is defined as "a subgenre of science fiction that emphasizes space warfare, melodramatic adventure, interplanetary battles, chivalric romance, and risk-taking." As far as I can see, the only thing that matched Weir's story to this subgenre is the risk-taking and maybe the melodramatic adventure.
I would honestly call it a 'survival film' instead of a Space Opera, seeing as though it hits all of the genre markers of those kind of stories, just set in space. It even has the trope often included in this genre, which is to have some sort of captain log, where the main character keeps track of their days spent alone and how they survive.
Honestly, I'd call 'The Martain' a 'Cast Away' on Mars instead of a Space Opera.