How is James Lee Burke so consistently awesome?

Year after year James Lee Burke publishes a "cannot put it down novel" that consistently blows away all crime novel competitors. How has he been able to keep his characters fresh after 18 novels? Each novel interlocks and mingles with the shared past of the previous ones but can also stand alone. He writes about an "edenic" Louisiana that slowly reveals the darkness lurking beneath the steamy surface. Yet, the question remains: how is he so successful? A few reasons:
1) His characters are stuck in a moral minefield - Take three of his lead characters, Detective Dave Robicheaux, PI Clete Purcel and Sheriff Helen Soileau. Each of them exhibits a tremendous amount of depth and growth throughout the series, yet we are constantly reminded of the basket of snakes each carries inside them. Any one of them could easily be "the bad guy" in any given novel and yet they remain fully committed to their own vision of justice, regardless of the consequences.
2) The setting constantly shifts - New Iberia and New Orleans represent a beautiful cesspool of mobsters, gangsters, corrupt politicians, racist oligarchies and dirty cops. Each novel introduces a new set of characters who are fully fleshed out and ready to unleash their own version of hell on Dave and his friends. There have been continual elements like the Giancano Mob Family and Lee Burke weaves their rise and fall through several early books. He never ignores the history he has created for his characters and builds upon it brilliantly - not many other writers have this ability. Robicheaux has undergone several life changes (and wives) and each one has been written with subtly uniqueness and understated power.
3) The Writing - Lee Burke writes so well your senses are completely assaulted. You hear, smell, see and taste every part of his world - no other writer can do this as well as Lee Burke. Occasionally he throws in a big twist near his endings but usually the books build to a forgone conclusion you may or may not accept. Nothing ever ties up completely and the good characters do not always triumph over evil. Often, his main "hero" is wrong in his assessment of the bad guys. Few other crime writers take these chances.
4) He is the only one who can pull off the slightly supernatural elements - Lee Burke occasionally has supernatural or mystical elements involving life and death in his books and surprisingly it always works. I have read other novels where the authors have tried similiar things and it does not work. For Lee Burke, it always does.
His latest The Glass Rainbow (number 18!) is a fantastic summation of the entire series. All the elements are there and the book is fantastic. The great thing about his series is you can pick it up anywhere and get a great read. It is not necessary to read from the very beginning, but, each novel has to be read, and fully enjoyed.