I don't usually review movies, but "The Martian" isn't most movies.
If you haven't read "The Martian," it's most aptly described as a combination between "Cast Away" (more sand, fewer volleyballs) and that scene in "Apollo 13" where astronauts have to build a new air filter out of random rubbish from their ship. It's a wonderful book for wonks, but I can't in good conscience pretend it's everyone's idea of beach reading.
The film -- as translated to cinema by director Ridley Scott -- adds in cinematography reminiscent of "Moon," another tale of a man left stranded far from home. And by fudging just a tad of the science (mostly by glossing over the most intense of Watney's many calculations), the film earns itself mass appeal.
Like most big-budget disaster movies (and hey, if one man being stranded alone on Mars isn't a worldwide disaster, I don't know what is) the characters themselves aren't really characters. No one wastes time trying to make you feel for Watney because he's Watney. You're just supposed to feel for him because he's struggling to survive on a desolate planet, with slim odds of returning to Earth. Which is pretty valid, and works pretty well.
"The Martian" isn't really about its titular character, any more than it's about the scientists scurrying about frantically trying to save him. It's about humankind -- humans as one cohesive unit, brought together by a big, strange outside threat that just happens to be the vast, untamed nature of space itself instead of an alien or what-have-you.
Save for a few cliche scenes thrown on to the end of the movie, the plot is largely driven by science: Watney has to come up with a way to feed himself (which makes it convenient that he's a botanist and not some heroic pilot instead) and a way to create water. If you've read the book, you'll know that these processes (or at least Watney's explanations of them) have been greatly simplified. If you haven't read the book and have nothing but intro-level chemistry on your side, you're going to be agape at all the science-y gobbledygook. But the pacing has clearly been timed out for a viewer with only a passing interest in the details: As soon as you start scratching your head, Watney has moved on to something else.
In her own review of the film, University of Melbourne astrophysicist Katie Mack points out that the creation of water is one of the story's biggest fudges. Scientists are now fairly certain that Mars has lots of water locked up in its soil, which would mean there's probably an easier way to get it than Watney's dangerous experiments with rocket fuel.
That's not the only place where science is glossed over to make life on a desolate planet even harder. There are some unrealistic obstacles preventing communication with NASA, and the entire premise of the movie centers around a very unlikely storm.
When I was in high school, my calculus teacher used to tell us to use "brute force mathematics" in a pinch. If you don't know the formula and the numbers don't look familiar, just plow through until something starts to work. "The Martian" is a movie about brute force botany, chemistry, astrophysics and engineering. It's a movie about people struggling to survive using the best tools they have; not guns or giant robots but science and ingenuity.
I recommend "The Martian" without reservation. It's a great time, especially if you share my proclivity for getting emotional about Mars rovers. But what excites me most about "The Martian" is that it's going to attract a wide audience, and I have no doubt that plenty of non-science-nerds will enjoy it, too. It's a movie where science is front and center, and where scientists -- including, for what it's worth, a refreshing (though not perfect) ratio of women and people of color -- are real and scared and incredibly brave. It's a movie about humanity where all the humans you see on screen happen to be scientists.
But I'm probably biased, because there's a whole scene that hinges on astronaut poop.