Cornwell went down the tubes, as did Jonathan Kellerman, but only after a lot of great reading. I was able to read Norman's 'Gor' series for about 7-8 books, but then he got too involved with slavery as the natural order...
However, I was able to read 93 of the 125+ "Destroyer" series, a delightful tongue-in-cheek send-up of the martial arts super-hero. I'll always look forward (I hope) to the next John Sanford although this last one was not quite as gripping as all the others in the 'Prey' series.
I'm hoping Parker's 'Spenser' or 'Jesse Stone' series will continue. They are perfect for 4 hour plane trips! Total immersion/finish in one read.