While time has made most of the suppositions about the planets obsolete, these are still readable as good old fashioned space operas. Our uncle gave us a set of these books when I was about twelve and I have read and re-read them many times. I snagged these from usenet a year or two ago and found them a pleasant trip down nostalgia lane.

Sad that these are no longer in print, but not sad that they are now available as ebooks.