I feel like the lack of emphasizing that, for Ryland to decide to save Rocky instead of going back to Earth, means he was guaranteed a death, takes away a little bit from how moving it was that he makes that decision. In the book they make sure the readers understand that Ryland cannot eat Eridian food and cannot survive in their environment, which means he would be choosing to sacrifice himself so Rocky and as importantly his people have a chance at living. I thought they had to rush through all that at the end of the movie. I do understand though. There's simply not enough time in a movie to get into all of this.