Frank Herbert only wrote six books (Dune, Dune Messiah, Children of Dune, God Emperor of Dune, Heretics of Dune, and Chapterhouse: Dune), sadly. His asshole son finished the series off with two books that are only worth reading so you can see how awesome Duncan Idaho and Miles Teg are. Although, thinking back on it now, perhaps I should read them again. I bet I'd have a whole new perspective on Feyd Rautha's athleticism and physical prowess.
I convinced myself to stop reading them yearly when I discovered the joys of other things in life. Like booze.