I felt a little robbed with Sandworms ending the first time I read it because of my general like for Paul as a protagonist over all the others, but when I went back and did a re-read from post first half of the series, it made sense and I appreciated it more. Yeah, as a writer I would have made a couple changes here and there, but I respect how it was laid and worked out. There was a plan, and it was followed and executed very well. Honestly, Herbert’s stuff is metaphysically dense and needs digesting sometimes. It gets worse when a guy like David Lynch takes a shit all over it just to fuck with your head and your senses.
It is especially fun if you line up parts of the Children of Dune mini series soundtrack at some points, especially during the final battle when Leto II returns to himself, listening to Summon the Worms and The Jihad bring it to life.
I only ever stayed with the main story, so I have no opinion on the prequel books or extra stuff.