I'm probably not the most qualified person to say this, as there are some people that read way more than I do here, but I have never read anything like Dune. It's hard to put it, but there is so much there that is different. It's "science fiction" but not in your current, common state. It's like post-future brutalism, in a religious fanaticism based world (and that's like maybe a 10th of it). On the surface it sounds more "boring" than your current traditional sci-fi book. The level of exposition, the ecology, religiosity almost make it an almanac of some sort, which is probably selling it short. I feel like I could ramble awhile and never really properly hit what Dune is, it just feels different. Hyperion may be my favorite science-fiction book so far, but I fairly often catch myself thinking about the imagery, or imagining "Dune".
I also say this as someone who has, so far, only read Dune itself. So I don't know how my opinion would change with the other books, but it's a special book. I could see how people maybe wouldn't like it, or think it has aged, but It's a hell of a book.