Book review: The Gap Cycle by Stephen R. Donaldson

[Please note that this is a review of the entire series rather than any individual book within the series.]

Stephen R. Donaldson is primarily known for the dark fantasy work The Chronicles of Thomas Covenant, which kicked off his career.  The Gap Cycle, however, is a space opera.  The sub-genre space opera is a form of science fiction traditionally characterized by a focus on grand adventure, melodramatic romance, a war of good versus evil, and characters rather than technology.  The setting of outer space tends to be used merely as a backdrop for the action.  The Gap Cycle is a space opera in a more literal sense, too:  The last four books in the series were inspired by Wagner's Ring Cycle.