Well, I just can't help myself. Dune is nowhere near a short story with 13 books and counting (<rant type="preemptive">Yes, I both count canon and non-canon, and for those of you who wish to discuss that, there are plenty of open threads on the dunenovels forum in which I even participate</rant>).
So, 13 books and in my opinion the greatest science fiction novel-series ever written. But what makes it so good? Is it the story, is it the imaginary work of the author, or perhaps something as insubstantial as the readers imagination.
Well, here's my view on it, but first a bit of history. I've approximately read all 13 books way too many times (+20 in all, for each book, though I don't get tired of them at all) and what I experienced at least the first 10 times for the first six books (by Frank himself, of course) was that each time I read it, I discovered something new about the books, the universe, or some new layer to the book - like a social layer, a political layer and every other sort of imaginable layer. This is part of what I like about Frank's works because that's true for all of his work, even the work not involving Dune in any way (it also seems to have passed onto his son, although not as much of it - but still an amount greater than most writers have).
To put it simply: Frank made a universe different than ours but the same as hours, just far far far into the future (approximately 22000 years before the first book starts, according to Dr. Attila Torkos, the Hungarian translator of Dune who made a time line which can be found on dunenovels.com). I'm not saying that a book has to be 22000 years into the future, or that it has to be an entire universe created from ours. I'm just saying that to write something good, you have to be there and take the reader with you, so to speak. And that's what Frank manages so well.
So, for all of you writers out there - that's all you have to do. So good luck with that..