Arrakis has been destroyed. The heirs to Dune's power have colonized a green world, and they are turning it into a homely desert. It's not so much a pitfall in the path of all governments as it is a delusion waiting for anyone who gains power. And I thought you would tell me something new. It combined a spy thriller with the theme of overpopulation.
Additonal themes are psi powers and total mind transference.
Herbert died on February 12, 1986. The last two novels in the Dune series develop a new and different story, which Herbert would have continued if he had lived.