McKillip is another one of my underrated favourite genre authors. She has a beautifully lyrical style of writing combined with solid characterisation and a sly sense of humour. Though she has written some science fiction, and some fantasy set in the modern world, the vast majority of her works are fantasy fiction set in that familiar pseudo-medieval world of forests, castles and magic.
She is probably best known for the Riddle-Master trilogy, written in the 1970s and comprising The Riddle-Master of Hed, Heir of Sea and Fire and Harpist in the Wind. I enjoyed these for their interesting and unusual hero, and the strong female characters (very important to me as a female reader of genre fiction).
Other books of hers that I have read and enjoyed include Alphabet of Thorn, In the Forests of Serre (one of my favourites), the two Cygnet books, and Ombria in Shadow.
I also very much liked The Forgotten Beasts of Eld, for the refreshingly arrogant and aloof lead character, Sybel, a woman who is really quite callous in using the love of a perfectly admirable man to plot revenge against the villain who has humiliated her.
The aspect of this book I particularly thought well done is the nature of that humiliation. Without getting on my soapbox (hah!), I cannot stand the default, lazy, thoughtless plot device rampant in fantasy fiction of using rape when the female lead needs to have a fall (don’t get me started on the worst example of this I have ever read, in Betrayal by Fiona McIntosh). McKillip here effortlessly comes up with something more original, more relevant to the characterisation, and in a way more devastating for Sybel than rape could ever have been.
More information about McKillip and her extensive works can be found here.

[...] you just revert to rape? Come on, put a little thought into it. I’ve already mentioned once the excellent alternative used by Patricia A McKillip. Another story (title and author escape me) had the villain turn the heroine’s best friend [...]