In case you don't know, Never Let Me Go is a book by Kazuo Ishiguro. While the book has a dystopian vibe, the story is very much about the friendship between the main characters. Even though it becomes evident that something is off about the school and the way these kids are treated right away, you don't really get a sense of what is fully happening until later into the story.
And that is my main problem with the movie trailer. I guess it is to be expected, but I feel like I've watched the movie after seeing just the trailer. Oh well though. I found the book pretty depressing and, while good, not as incredible as some people seem to think. Books are funny like that. Hopefully the movie will be good.