I read Dune in middle school, as had a number of my friends. I also watched the original David Lynch* Dune movie (theatrical and extended), been alive to play the Dune RTS game, watch the SyFy mini-series, and now seeing the new movie. (This is not to mention the Dune RPG getting most anticipated TTRPG from ENWorld how many years in a row?) I'm not entirely sure how its cultural impact has been minimal, especially among "geekdom." It's impact may not be as much of a pop cultural phenomenon as Game of Thrones, but its legacy has clearly been more enduring.
* David Lynch's involvement in the Dune movie is also part of its enduring legacy, particularly among Lynch fans.