I've had to think for a couple of days now about how to express my feelings and impressions of Dune upon completing it, and I think I have it right now...
Finishing Dune for the first time one gets the feeling that you've missed something. Maybe it's my training as a historian, but I get the feeling that I've read a historical account of the utmost importance, but find myself missing parts of the story, certain angles, would be a better way to put it. It leaves you yearning for more information, more completeness. But here's the odd thing: you also get the feeling that those missing pieces, those alternative viewpoints are in the SAME book. Herbert's son says in the afterword that his father once said that Dune was meant to be a story with re-readability. That it was composed in layers so different that the story could literally change every time you read it - and I believe it.
Story Layer 1: Religion - Dune is the story of the long-awaited Messiah figure Maud'Dib, sent to the hostile desert planet of Arrakis to lead an oppressed people to freedom and to end the vile and corrupt rule of the Harkonnens and avenge his father, while restoring the universe to it's proper path.
Story Layer 2: Environmentalism - Dune is the story of a world destroyed by desertification. The protagonist leads a group of conservationists intent on restoring the world to a paradise, but in order to do so, must sacrifice the most valuable substance in the universe.
Story Layer 3: Politics - Dune is the story of a band of nomads who resist the maneuverings of a powerful nation group and try to gain ascendancy in a galaxy-wide empire by controlling the lifeblood of that civilization: Spice (cough, cough...oil...cough, cough). Dune also examines the fallibility of leaders, even charismatic and intelligent ones.
There are obvious morals to each of the stories and levels of wisdom to explore in each.
What makes Dune a classic is not just the labor of imagination on the part of Frank Herbert (it is the science fiction equivalent of Lord of the Rings with it's intricate subplots and well developed background, including native languages; you could literally make substories or entirely new novels out of background figures and events mentioned only in passing), but it's malleability. The reason this story has remained a giant in the genre of science fiction for so long is because it literally changes with the times. My readings of the environmental and political layers, for example, are a result of the things that I see as valuable and important in my own cultural and historical context: global warming/the "war" on terror. The genius of the novel is that it accounts for countless such contexts and thus will never be "old" because it will always have something to say about contemporary events. What would I take from Dune if our society ever moved to the point where we were not dependent on fossil fuels and had a reliable, renewable source of energy?
As a side note, Herbert is an intellectual giant and certainly knows how to turn a phrase or two. I found myself writing down lines packed with timeless wisdom and that just sounded cool, until I ended up with like 3 or 4 pages worth. I know of no other author able to make me do that besides Chuck Palhaniuk. Both authors, though very, very different in style and content seem able to capture simple truths and reveal to you things that you already know in breathtaking ways. It makes me feel inferior as a writer and just a general observer of humanity.
Needless to say I will be reading this again and I look forward to reviewing it again and comparing my afterthoughts. Highly recommend for all, especially people like me who simply read superficial, guilty-pleasure sci-fi (like Star Wars - you know it's good!).