I agree. I found the sequels both not as compelling and harder to read than the original (the notable exception being Dune Messiah, which was still quite interesting and closer to the original): Plans within ploys within ruses within plans for pages on end, contemplations of a literal Godking in an even more distant future made the later storyline very difficult to follow at times.

However, while the first novel was the most digestible and most intriguing plot-wise, it is the sequels that explore the philosophical, political and social subjects of the original much more deeply. In a way the sequels are sometimes more like (huge) essays on various philosophical topics that merely use the original story as a backdrop.