Besides, is Dune hard to read?
Dune is not a terribly difficult read. It's long - 412 pages - and has a large cast of characters and several sub-plots to keep track of, but it is well written and an excellent example of a world-building novel.
Subsequently, question is, is Dune set in the future? Dune is based on a complex imagined society set roughly 20,000 years in the future. The setting is the year 10,191, and human beings have spread out and colonized planets throughout the universe.
Regarding this, can you read Dune as a stand alone?
Like people said though, you can absolutely just read Dune by itself and enjoy it for the masterpiece it is. But read the first one it's own, it's fantastic and if you end up reading the rest of then it's probably because you were so drawn into the universe. The first book is amazing, the rest are really good.
Is God Emperor of Dune worth reading?
Jo Walton once wrote, fairly, that each of Frank Herbert's Dune novels is about half as good as the one before it. By my math, that makes God Emperor of Dune (#4) about 12.5% of a classic, but it's still worth reading. It's about the ruminations of a man who turns into a worm, but it's worth reading.