Sadly, I think "Dune" is being seen as a cash cow, and all 6 of the preludes have been rushed out unfinished, or so they seem. The plots generally are pretty good, and if you can just focus on them, the books are enjoyable. But they suffer in a few ways. The bad guys are too evil. Both the Harkonnens in the "Preludes" like this, and the Titans and machines in the "Legends" series are evil tyrants who spend half the books enjoying grisly torture. It's rabidly overdone and dimishes the bad guys in the process. More irritating than that (to me anyway) is that the book doesn't seem to have been proof-read. The number of times a character's name appears where he/she should have been used, making you think that we've changed to a different person when we haven't, are almost beyond count. It's a real pity because there are some good plots and stories here, much better than any of the sequels Frank Herbert wrote, but they just don't seem to have been completed properly before publication.