The Forgotten Beasts of Eld is gorgeous and lush and precise and suprisingly dark. At least, I've read it a dozen or more times and the darkness always surprises me. Beneath the lyrical language and the carelessly perfect creation of myth and the details and the friendships there are really astonishingly horrific things happening in this story. It's much like myth, or folklore, or any unexpurgated collection of fairy tales in that way.
Not that the experience of reading it is horrific, because it's not: it's been one of my comfort reads for decades now. But this is a book where the darkness is as deep as your own knowledge or inclination to fill in the gaps. It does that trick the very best fantasy intended for young people accomplishes of saying things in a way that makes them clear to people with the emotional or real-world knowledge to fill in the details, while eliding the specifics to something comfortable enough for those without that experience.
There are dragons and talking cats and enchanted woods and tall white towers and the wars of princes, ancient riddles and broken hearts and friendship and betrayal. Parts of the language feel like Welsh mythology to me and parts feel like Carl Sandburg's poetry, all full of white birds and flowers and love and questions.
Patricia McKillip is still writing things that are luminous and dark and deep. This isn't a bad place to start.