Frank Herbert is one of the most beloved science fiction writers of all time. The Dune books are almost exclusively responsible for his (in my opinion) well-deserved reputation. The Dune series in chronological order is a bit hard to list, because readers are divided on which books are the “official” books in the Dune series, and which should be excluded from the official.
The reason is that Frank Herbert only wrote the first six books. Then his son Brian took over and expanded many elements of the series, including prequels. Regardless of which books you decide to include in your own list, I recommend starting with the original. Dune was Frank Herbert’s attempt at synthesizing his views on religion, philosophy, ecology, violence, mental strength, technology, addiction, and more. Sounds pretty intense, doesn’t it?
It’s true. The Dune series takes itself pretty seriously. It is not heavy on laughs. Sometimes it is not even heavy on cohesion, but the reader who can stick with the plot will eventually see most of their questions answered. Also: these are not small books, and yet I recommend trying to read through each one as steadily as possible. If you dip into Dune here and there you will lose track of the many characters and plotlines.
I believe the best four books are
2. Dune Messiah
3. Children of Dune
4. God Emperor of Dune.
A lot of people give up long before they hit part four. Then they give up because God Emperor gets seriously strange. But Herbert’s legions of fans are not put off by the bizarre shift in the plot. If you have ever met any diehard fans of Dune, you will know that they take the books pretty seriously themselves.
My final advice is to enjoy the books from the Dune series on your own terms. If you want it to be a philosophy book, it can be. If you want a treatise on ecology, feel free to look at it that way. But if you just want a great adventure story, there is nothing wrong with that either. Frank Herbert’s writing can be whatever you want it to be.