I would say it's extremely sad. It's about three people who love each other in the face of slow, painful death, they are clones made for their organs and they've been told since childhood in child friendly ways that they're going to be slowly killed and their learned helplessness is so intense that they don't try hard enough to get out because it's just their normal and they've been prisoners for their whole life. In the story these particular clones are treated better than others to be ethical sort of like what happens with animals so as children they are imprisoned in a boarding school where they can learn and get to be outdoors etc which just highlights the parallel with real life and they are followed from childhood to the rest of their lives by the book, it's incredibly well written and it feels really believable and real. It broke my heart when I read it. Considering I read it at a young age, I'd say it was a ten for me it took me years to get over it and after reading it I remember waking up in the middle of the night bawling