This is an SF novel by a mainstream writer, but nevertheless it's brilliant.
Kathy H, the narrator, is a carer who will soon become a donor, and she has, according to her unreliable first person voice, led a life of privilege. She was brought up at Hailsham, which made her special for a start, and then she has been allowed to be a carer for twelve years, before becoming a donor. The book is written as memoir, and it uses the language of privilege and nostalgia to write about terrible things. Actually Kathy is a clone who has been brought up merely as a walking organ bank, and her privilege and specialness consists of the fact that she has had a slightly better life than some of the other walking organ banks. She thinks she's writing about her friends and her romances and how lucky she has been, and really the world and her life is slowly being revealed to the reader as awful.
Kathy's first person voice is absolutely compelling -- I couldn't put the book down, and read it at one sitting even though that gave me a very late night. Her personality, her naivety, her careful thoughtful observations, her slight primness, come over in ever well-chosen word. On the writing level, this is a masterpiece.
This isn't paced like an SF book, and the revelations are not handled like an SF book, and I'm not at all sure the science works (they give four organ donations and then either die or "complete" in their term, or are kept barely alive with no more pretence of actual human life for other donations) but this is SF, this is doing what SF does, it's turning the world around and showing us another face.
Some reviews call this "near future". That's nonsense. It's specifically stated that it's 1990s England, and an alternate reality where the cloning became possible shortly after the war.
Other reviews complain that people don't put up with things this way, they rebel and try to run away. Well, sometimes they do, and some of the other clones may be doing, but some people always accept and go along with expectations. Kathy looks forward to having more time to think about these things when she's a donor. She's thirty, and we know, and she also knows, sort of, that she'll be dead in a couple of years. There isn't any time, and what she has been offered is painfully thin, as lives go. And she accepts and goes on with it because that's how she is. I have no problem with this. The novel with the revolt in it would be a different story, like Budrys wanting Nineteen Eighty Four to end with Big Brother overthrown.
Of all Ishiguro's other work, this is closest to The Remains of the Day, which also has a first person unreliable narrator, and also deals with power and possibility. If anything, this is even better.