So... The Martian is a really, really good adaptation. The novel was easily the best hard SF book I've read this year, and the movie caught pretty much every aspect of the book without coming off as talky, poisoned-by-CGI or in any way superficial. After getting past the weirdness of Chiwetel Ejiofor being cast as an Indian-American NASA higher-up, and snickering about how Mackenzie Davis is going to be stuck playing techno-punk pixies until she's fifty, I was OK with the cast. Coming into the movie, I was concerned about my cordial dislike for Matt Damon causing problems, but he disappeared into the role, and barely looked like himself for most of the film.
I see Drew Goddard wrote the script, and he did a brilliant job of adaptation, because I didn't spot a fleck of him or his Whedon-stable influence in the movie: being that transparent is a real skill. They excised some of the novel's set-piece disasters, but if they had tried to film all of that, it would have added another half-hour to the length, and probably overwhelmed the audience. It was *just enough*.