I think everyone who recognizes Frank Herbert will know Dune and its universe, which was synonymous with him. Six books, and a saga left unfinished that was and continues to be fleshed out by his son. But Frank wrote a great deal about Dune, but he wrote many other books. I'm reading The Green Brain, he also four books about life forms on a planet settled by humans (Destination: Void), and dozens of other stories about Native Americans, genetic tampering, and the power of nature in general. I've never been much for Herbert's writing style, but his respect for the living earth and his understanding of ecosystems is a little overwhelming.
What impresses me about Herbert is simple. Arthur C. Clarke was a brilliant man who came up with ingenious ideas about star travel, time, and God. Asimov gave us stories about robots and a new technology to foretell the future. A dozen other Sci Fi writers have created their own niches in the genre, but Herbert did it by focusing on a respect for nature. Every story touched on some aspect of it. Of course to read Dune is to be familiar with every aspect of the subject - but he went into so much greater depth in his other works. Maybe not as brilliant as the two grandmasters of science fiction, probably not as interesting in his plots. His characters have depth, more so than Clarke's, but they are not much fun to read about. What he did have was a singular vision of the future and the present and he used his imagination and his knowledge in novels to spread that vision to science fictions readers throughout the world.
I have made a point of reading all of the Dune novels so far, and collecting all the other stories he published. The technology is generally not that interesting (apart from their form of space travel) and even the theme of the destined hero is not done as well as it might be. What attracts me are his insights on all aspects of a planet's natural workings and his thoughts on genetics, politics, and even religion. When I read other science fiction writers I am reading intelligent men who found subjects that an audience might find appealing. When I read Herbert, it is a man who had an overwhelming passion and would not have cared if his following had never exceeded dozens. Integrity like that I can get behind, the writing doesn't have to be as good, the plots and characters don't need to be as strong. Reading Herbert is worth it.