Sunshine by Robin McKinley. To quote Neil Gaiman “It’s not quite SF, and it’s not really horror, and only kind of a love story, and it’s all three while still being solidly Fantastique.”
Robin McKinley in my favorite author. There is no runner up, there is no debate. Since I first read The Hero and the Crown when I was about 14 I have devoured everything she has written. Sunshine not only did not disappoint, it blew my mind. Most of McKinley’s work is classified as Young Adult and this was her first book that was written for adult audiences. Not to say that adults can’t enjoy YA books, it’s my favorite genre, but this was her first book that was targeted directly at grown ups and featuring more material verging on an R-rating as well as being a more challenging read. I didn’t know that when I picked it up but I knew it before I was 20 pages in.