Let's briefly discuss the book, first. If you haven't read it, I recommend doing so. In short: near-future astronaut Mark Watney gets stranded on the surface of Mars, and must figure out how to stay alive using only the limited resources at hand. This is hard science fiction. Weir meticulously researched all the problems facing Watney, without giving him magically advanced technology to defeat them.
The story is largely told through Watney's journal updates, which read remarkably like following a brilliant engineer's blog while he solves fascinating problems. Weir also infuses Watney with dry humor and an unwillingness to be told that the right way is wrong. For being so dense with science and engineering, the book manages to have a rapid pace.
Fortunately, that pace made the transition to film a bit easier, as did the book's narrative form. Watney's thought processes tend to be spoken, rather than a typical internal monologue, and this keeps it more conversational and brief. In the novel, when Watney has to "do the math" — for example to figure out the hydrogen levels in his living space — you follow along as he actually does the math, then as he develops a procedure to safely lower those levels. The movie tackles this complex scene by making him discover the problem right when it begins, with a small amount of hydrogen igniting dramatically. It keeps the science and the problem-solving, but conveys it quickly and moves on.
That's the real triumph of this movie's creators — they accelerate the plot while maintaining the book's love and respect for science and for thoughtful engineering. They embellish for interesting visuals, like the martian wind, and for dramatic license. But they never go over the top. It's... refreshing, to say the least.
One thing the film does even better than the book is bringing intensity to particular scenes. It's one thing to read Watney's account of how he dealt with an emergency in past tense — it's another to see it as it's happening. The first scene of Watney alone on Mars is incredibly tense and visceral.
This is largely due to Matt Damon's performance as Watney (and to Ridley Scott, for enabling that performance). Damon does a great job coming off not as a movie superhero, but as a funny, capable guy you might run into at your local makerspace. The other roles in the film are well cast and performed, too. Jeff Daniels as the director of NASA is the closest the movie gets to having a 'bad guy.'
He's the one who tends to raise the practical and ethical questions surrounding Watney's predicament. How many resources should be allocated to helping a single man? What will be the cost to future missions if they don't? They're impossible questions to answer, but they deserved to be brought up and debated.
One of the big reasons to see this film is for its cinematography. If you're a space buff, you'll really enjoy the long, lingering shots of the Martian surface. The graphic artists really deserve commendation. They make the landscape look both desolate and fascinating. They had lots of source material to work with from all the rovers and orbiters we've sent to Mars, and they used it to fill each scene with incredible detail. Look carefully and you'll see one of Mars's lumpy moons in the background of a shot on the surface, or a dust storm slowly flowing across a vast mesa when looking down from orbit.
The Martian, much like Apollo 13 twenty years ago, inspires us to cheer on our civilization's brightest scientists and engineers to solve hideously complex problems. NASA has been falling all over itself to help promote the film, and for good reason. I think the reception of this film will show support is still there from the general public to go and do really challenging missions. The Martian the best movie I've seen all year, and I highly recommend it.