Forget the Sci-Fi angle; it's insignificant except as a stepping-off point for a story that reveals great truths: That life is short, your choices have consequences, and at the end none of us may feel we've had enough time to love, or just get things right. But I can safely say... If you interpret your movies literally, you will not like this film. If you need action, a fast pace, explosions and special effects, you will not like this film. If your idea of a great movie is Inception, forget it.
On the other hand, if you can appreciate a fine story by Henry James, Edith Wharton, or Katherine Anne Porter, this film is made for you. If you enjoyed Todd Haynes' lovely melodrama, Far from Heaven, or Oren Moverman's powerful movie, The Messenger, or Tom Ford's poignant film, A Single Man, you'll love this picture. The story addresses themes of love, longing, jealousy, betrayal, courage, atonement, and perhaps most important "acceptance." The film also asks us to consider the "morality of science," and some might find this aspect chilling, but to me the larger human themes overwhelm this one.
When I saw Never Let Me Go, the theater was about one-third full, but probably one-third of these folks walked out by the half-way point. And, surprisingly, the couple sitting behind me got up and walked out 10 minutes before the end, once they were convinced (revealed by their groans) that the story would not have a happy ending. Apparently, they were looking for the "feel good movie of the year." Sadly, they missed the most extraordinary and beautiful ending -- most of the emotional power comes in that last 10 minutes -- but then I suppose they wouldn't have understood it. But to me, Never Let Me Go is the "feel good movie of the year," precisely because it tells the truth: life is beautiful because there are hopes and dreams, love and loss, tears and tragedies.
One final note: Keira Knightley and Andrew Garfield are excellent in their roles, but Carey Mulligan is the standout -- she shows a wisdom and weariness far beyond her years, and handles difficult emotional material with a sublime restraint that makes the whole thing work. I feel we are witnessing the early work of the next Deborah Kerr, Sarah Miles, or Vanessa Redgrave.
This is an excellent film, one of the best of the year, and not to be missed by those who appreciate depth and literary quality.