I did however mention one novelist that I admire whose series actually grew stronger as he went along and that, of course, is Patrick O'Brian. After a brilliant opening novel Master and Commander (which someday should really be made into a film)* there was to my mind a falling off in quality until the excellent The Far Side of the World and the extraordinary Reverse of the Medal where Captain Aubrey gets convicted of rigging the stock exchange and is then struck off the navy list. The next five books in the series are as good as anything in modern literature. In particular I loved The Thirteen Gun Salute where almost nothing happens at all and the principal villain of the entire fleuve is actually killed off-screen as an aside. The Thirteen Gun Salute's metaphoric and emotional heart is a sedate walk up a series of steps to a ruined Buddhist temple in a Malayan jungle. This doesn't sound so awesome, but trust me, somehow, it is. The sequel to Salute is the sublime Nutmeg of Consolation where, again, almost nothing happens but for a deep exploration of the main characters' psychology and character. Wonderful stuff. The final book in this quintet is The Wine Dark Sea where HMS Surprise sails over the boundless Pacific for page after trance inducing page, while Stephen Maturin observes sea birds and looks after the declining mental, physical and spiritual health of his crew. The Wine Dark Sea flirts with genius in nearly every chapter and attains the kind of brilliant lyrical intensity you don't normally associate with historical novels or sea stories.
O'Brian wrote four more books after The Wine Dark Sea and they, alas, are not quite up to the same standard as the previous septet, but, Patrick O'Brian, at least for me, is the exception that proves the rule of the serial novel.