If all Watney ate were potatoes, wouldn't he develop a huge belly like the starving children with protein deficiencies or a pirates's black bruised scurvy? No, Because the reader knows that he had lots and lots of multiple vitamins to keep him healthy. What he lacked was raw calories. Thank goodness he was a botanist who could grow these.
Watney's trip to the future site of the next Mars mission was easy peasy on the screen. No major sand storms to interfere with his solar panels and tip over his vehicle. No back aches from the manual labor to prepare. Where was the cool bedroom he'd made in the book? Heck! Once Damon found an easy way to communicate with Earth, he never lost it. The movie was entertaining and interesting, but it lacked the obstacles and understanding that one gets from reading the book.
Although author Andy Weir claims to be the ultimate science geek who enjoyed working out the ins and outs of a mission to Mars, he feared the science discussions would bore the average reader. I, however, am that average reader who is not interested in math nor science yet never grew bored with his book. After all, how can one get bored with a book whose first line is, "I'm pretty much f*cked," and the first page grabs the reader with the knowledge that he's absolutely right!
Go on and see the movie, but before you do, read the book.
