This review about the Dune series as a whole:
The first book sets up with great world building and introduces many themes and topics, this allows many later books to flourish and forces the reader to engage, however it also can be overwhelming and can be confusing for readers, for this reason I recommend reading the book over a shorter period of time as previous details may be forgotten.
The books 2-3 retain a similar theme and are a direct continuation of the first book.
The 4th book is the start of thematic changes, this feels refreshing. This continues in the 5th book and is very prevalent in the 6th book where the theme of the book has completely changed. The last books feel as if they are a different story and are not part of the same story.