I loved "Remains of the Day" and "Never Let Me Go", but didn't finish "The Buried Giant." The first two aren't fantasy, but IMHO they're much better Ishiguro.
As for "literature-y" fantasy, I'd agree with others here to look at magical realism, e.g. "One Hundred Years of Solitude." But my opinion is probably crap -- some of my fantasy favorites are Tolkien's "Silmarillion" and "Lost Tales," which probably don't qualify as "great literature," but show some amazingly thorough and vivid world-building.
As for "literature-y" fantasy, I'd agree with others here to look at magical realism, e.g. "One Hundred Years of Solitude." But my opinion is probably crap -- some of my fantasy favorites are Tolkien's "Silmarillion" and "Lost Tales," which probably don't qualify as "great literature," but show some amazingly thorough and vivid world-building.