My wife (a botanist) and I just got back from watching The Martian. I laughed, I cried, I totally want to get her a "Best botanist on this planet" T-shirt.
If you've read the book, the movie stacks up quite well. They cut out quite a few of the engineering challenges that were detailed in the book. Most of these edits are in obvious places where the pacing would have slowed the movie down too much. For me, right after seeing the film, there are only two changes that really affect the feel of the narrative in comparison to the book. The first is related to Watney's accident with Pathfinder and the second is related to the attempt to rescue Watney after he leaves Mars. The very end of the movie does a better job providing closure for all of the characters than the book did.
Speaking of characters, that's something else I appreciated about this film: the inclusion of under represented groups, playing characters that have agency. I would suggest that there are probably women of color who work at NASA and in the future, I hope they actually do get to play important roles in getting humans to Mars. I also would think it would be easier to pass the Bechdel-Wallace test, given how much time is devoted to a big spaceship with two women aboard, but there's only one scene where the film might almost pass. Regardless, this movie doesn't take too many shortcuts when it comes to presenting different people as, well, people.
Overall I give it 4.5 Martian Potatoes out of 5 Explosive Decompressions.