McKillip's fairytale style of writing is exceptionally adept at soothing the reader into a trance-like state that allows the story to flow and twist about in a very Grimm sort of tradition. The characters are not especially deep. Very few details are revealed about the inner natures of even the main protagonists, but it allows the story to be what it is. You don't fall in love with the Prince and Princess the way you normally would in most of the modern fantasy dramas; the "bad guys" are not necessarily "bad guys" and everyone's faults earn more mention than their virtues.
The story is about a situation that weaves together classic fantastic problems and possibilities and allows the characters to work it all out in what might be viewed as a highly predictable fashion, but is nonetheless altogether fitting for the choices offered. Don't ask more of the characters than what is presented - let them be what they are and simply lose yourself in the fairytale.