I finally got around to reading Dune. I burned though it pretty quickly and loved it. For some reason I can't get into the other books in the series. For now they mock me from their spot on my bookshelf...
Dune, followed by a 1-5 year pause, followed by Dune. Repeat until death.
You may, if you wish, throw in the first hundred pages of a different Dune novel every ten years or so, just to remind you of the correct sequence.
My advice: Even though Dune 2 is a good book - it's best to stay off the slide downwards or you'll wind up like me reading all of them and wondering if I could get the time back.