Sci-fi is not a genre I would ever choose to read. If I had known the book was free on line before it was published, it still wouldn't have made my to read list. I loved this book. I could not put it down. Mark Watney was funny - granted it was generally junior high boy humor - but he was funny. Some reviewers said this wasn't believable - he didn't get depressed, etc. Astronauts go through rigorous psychological testing individually and depression / inability to function meant certain death. Mark Watney's log entries did occasionally say things like 'I am so f#@K%d.' but he knew that he couldn't stay in that thought. My favorite line in the book - not a Mark Watney line - is "I'm space paparazzi now. The attitude comes with the job." Mindy Park. I highly recommend the book, I have not seen the movie.
Basically friends have been raving about this for months, I actually didn't love it as much as they did but I did enjoy it a great deal.