Dune has that strange feeling of unreality about it that I first experienced with Chronicles of the Witch World, published around the same time as Dune, and really the two series seem to share a lot of features at first blush. 
 Let me explain, by "unreality", I mean the sense of feeling a *compulsion* to read, and the sense of being in a separate time and place from my body sitting in my home. 
 As for their similarities, the Bene Gesserit have a lot of the same feeling of the witch council of Estcarp, and Paul and Kemoc of the Witch World share the trait of joining in what are ordinarily feminine mysteries. 
 What surprised me most, coming from a background of "um, there's worms and sand, and I guess it's the reason all the Star Wars EU writers were obsessed with spice mining", was the emphasis on religion and ecology.