All of his books are sad! Or maybe sad isn't quite the right word, maybe poignant, or affecting.
I enjoyed the book although would put it some way down on my list of favourite books by this author, which would begin with Remains of the Day and The Unconsoled. It had some of the same sorts of logical flaws that bothered me when I read Never Let me Go, his other sci-fi inspired work. Without getting into spoilers, I didn't feel the purpose of the robot companions was convincingly established, and I was also bothered by the mechanics of the children being 'lifted'. But that may be because I'm a scientist and need science fiction to make scientific sense - I'm not sure that sort of accuracy is what Ishiguro is aiming for, and probably most readers either!