I’m a fan of Guy Gavriel Kay. Not a big fan, but a definite fan. I recently re-read both The Lions of Al-Rassan and The Fionavar Tapestry recently and realized two things. First, Lions is a really good book. Second, Fionavar is a well-written trilogy that borrows so many elements from so many well-known fantasy novels that it actually detracts from the story.
Just off the top of my head, I specifically noticed ideas taken from Joel Rosenberg, Stephen Donaldson, Susan Cooper, Lloyd Alexander, and Roger Zelazny. No doubt there were more; I’m not including the obvious Arthurian theme, which frankly I think the books could have done just as well without. I think in the hands of a lesser writer, Fionavar would have been a lifeless Frankenstein’s monster, but it’s interesting to see how Kay’s skill is such that he can weave a reasonable story out of so many begged, borrowed, and stolen threads.