Never Let Me Go by Kazuo Ishiguro.
I thought it was brilliantly written (how does an adult male get the voice of a young girl/woman so perfectly?) but I'm not sure I'll read this one again. It was haunting, but in such a subtle way that you don't really realize how horrifying it all is until you've finished the book. And now I can't sleep. I kept waiting and waiting and wishing for a turn of events, for things to change and become better & for the characters to rise above, take action, do SOMETHING but it never happened. At first I felt cheated, and now I just feel so uneasy and profoundly sad. The main thing that's clear is that Ishiguro is a master craftsman of his work.
I think I'll read his earlier book, The Remains of the Day too. I've heard wonderful things about it.