The very best fantasy is the one that is in touch with the sense of mystery. It is that sense of melancholic mystery tinged with an old knowledge that is the hardest to create and the most satisfying to read. The reader recognizes it in the pang of sadness he feels as he closes the last pages of the book. It's a sadness that stems from a recognition of the old magic.
The old Russian fairy tales capture this sense of mystery very well. "Vasilisa the Beautiful" is an excellent representation of this type of writing, as is Finist the Falcon. It's the eeriness of the beautiful maiden carrying a lamp lit in the head of a skull while being set these apparently insurmountable tasks that haunts and excites the mind.
Jean Cocteau's "La Belle Et La Bete" is another perfect example. Who will ever forget the anguished Beast's smoking hands, the music of extraordinary timbre, the sadness of an elegant Belle?
Oscar Wilde's "The Nightingale and the Rose" provides yet another example of this sort of prose.
Green Rider (but none of its sequels) has a touch of it, too.
Several of Peter S. Beagle's stories in 'We Never Talk About My Brother' have this quality and his book 'The Last Unicorn' epitomizes it.
But I have yet to see anyone capture it as well as Barbara Leonie Picard does in her 'Selected Fairy Tales.' Such an unassuming title and yet every story bears such deep knowledge, commiseration with and sympathy for the human condition.
The mystery lies in that which is inexplicable but true; the story could not have been told in any way other than what the author described it to be. It operates on older principles, the values of an age where magic was free and roamed the earth, where sacrifices had meaning and each creature went to meet his destiny with an open heart.