What does one say about a book that has stuck with one for over 15 years now? It remains the right book at the right time and I wish it was better known because it feels genre-defining in ways I still can't put my finger on.
McKillip's approach to both magic and character is part of the fabric of 20th century fantasy that led to some of the amazing work that was done in the 21st century.
Someone should talk trilogies and look at Tolkien as inspiration for both Guy Gavriel Kay and Patricia McKillip and how both of them, while inspired by LOTR, evolved those ideas in radically different directions. Both are obviously indebted to Tolkien, but neither is derivative. And both strike me as important cornerstones in a history of fantasy, even if Riddle Master feels like it's not as well-known. (Influence and name-recognition and the relationship between the two is ALSO an interesting conversation to have about fantasy...)