Frank Herbert is a good writer with a compelling artistic vision. The world and characters he created are fascinating, and the book has that gripping quality that makes one keep turning the pages to see what happens.
The book is worth reading, but with the caveat that you should not expect a traditional story. From the first chapter, the main character is defined as the privileged son of nobility, heavily trained in a mystic art that has changed his mental processes in fundamental ways. He is immediately set up not as a character but as a force of nature or destiny. There was no way for me to relate to him, even though I have had years of martial arts training that mirrors the kind of discipline he has learned. He is just too different, too removed from humanity. So the entire book ends up being not a story about a protagonist, but an anthropological study of events that happen in totally foreign cultures to people with alien thought processes. I am not put off by that, but I imagine many people would be.
By the end of the book, it is clear that the main character is also not a protagonist in the sense of doing anything good or changing the world in a positive way. He is consumed by his culture, his powers, and his own legend, becoming an empty shell of a man just like the people who blindly follow him. He acts randomly and senselessly, tempting death for no discernible reason. After his forces win the final battle and his victory is secure, he invites a potential assassin to kill him with poison, and then arranges a knife fight with another nobleman.
I got the sense that he was playing with his own life, testing the limits of his precognition with nihilistic abandon. All of his visions have shown him that he is incapable of really changing anything, and they are also unable to help him navigate any of the critical dangerous moments in his life. He has powers that are the result of 90 generations of careful training and selective breeding, and they end up being worse than useless.
Despite his earlier efforts to stop the process, he ends up promising to unleash his armies on the galaxy and create a terrible jihad, one that will make people think fondly of the brutal and ruthless actions of the armies of the emperor he has just defeated. The galaxy has simply traded one evil overlord for another. The whole rotten system is perpetuated, and the main character has become a copy of what he hated.
The only character in the book that I felt any connection to or sympathy for was Princess Irulan, the person who narrates the blurbs at the beginning of each chapter. She comes across as an intelligent person with much potential, who is abandoned to a life of loneliness and neglect by a 'hero' who sees her entire existence as nothing but a tool for attaining power. She is trapped in a brutal, decadent culture that denies individual liberty and potential, and she has seen someone who is capable of changing that but did not.
It is possible that this book is a Watchmen-style deconstruction of the epic hero genre. If so, it is a good one. But it is also possible that the book is a confused mess that straddles the fence between genius and madness. I am inclined to think the latter, because there are so many things that simply don't make sense. The plot and setting of Dune are like soap bubbles: if you poke them or just look at them too long, they disintegrate.
Despite the fact that humans have interstellar travel and all kinds of futuristic technology, all of the battles are fought with knives. The entire military system is built around knife fighting, and the key to political power in the galaxy is to have the best knife fighters.
The author tries valiantly to explain this and other things away with cultural and technological factors, but it just doesn't work. A good science fiction writer starts with some technology, and then explores the consequences of that technology to see where it will lead. Herbert attempts the reverse. He has a vision of what an interesting world looks like, and then tries to invent a combination of technologies that produces the desired effect. But he just can't do it, so the whole thing just ends up looking silly.
(Note: If you have never read Dune, you will probably want to stop reading now. None of what follows will make much sense. It is a long, detailed, geeky complaint of how the author violates various rules of science and ignores military strategy and political realities.)
The knife fighting is justified by the fact that people have invented personal shields that can stop all projectiles, but can be penetrated by a slow-moving blade. These shields can also stop poison gases, and can presumably stop shrapnel and the concussive force of explosions.
Leaving aside the fact that it is practically impossible for anything to stop all that but be penetrated by a knife, there is the crippling flaw that the shields are invisible. This means that they do not stop any light in the wavelengths that the human eye can see. A laser in that range of wavelengths, of sufficient power, could easily flash-fry skin and boil blood. And it is clear that the civilization has the ability to easily produce that kind of power.
Even without lasers, there are plenty of ways to get around the shields as described in the book. There is no indication that they provide any thermal insulation. If you dumped a good heat source, like a wad of burning thermite, in the vicinity of a shielded soldier, you could easily roast him alive. A single napalm bomb would take out dozens of shielded fighters. Even a simple molotov cocktail would probably do the trick.
And why knives? Rapiers would work much better. And for large-scale battles, a close formation of well-drilled pikemen, or a phalanx of guys with shields and swords, will always defeat an unorganized mob of knife wielders, no matter how good the knifemen are.
Even if you accept the knife fighting, there are other problems. The civilization can create extremely efficient anti-gravity units called suspensors. These are widely used, and a small portable suspensor that fits in a backpack could lift a human being. So why is it that their airplanes use jets and flapping wings? Why don't people always have suspensors built into their clothing, so they can fly at will, or at least jump really high? That would be a big advantage in knife fighting or any melee combat. But all combat stays on the ground.
Going back to the shield generators, it is repeatedly shown that when a 'lasgun' hits a shield, the shield generator explodes with enough force to destroy everything in the shield, and often much else besides. The lasgun also explodes with enough force to kill the wielder. This seems to be true, no matter the size of the lasgun that hits the shield. This effect was actually used in battle, to generate a massive explosion when a personal sidearm hit a large shield.
And yet, fortreses are routinely protected with massive shields. This means that it is always possible to destroy any fortress simply by having one man zap it with a pistol. The guy who shoots it will die, but that is a small price to pay. It is explained in the book that armies never do this because 'it would be impossible to prove that atomic weapons were not used' and the attacker would be therefore be destroyed by everyone else. But what stops a random madman or fanatic from doing this? Lasguns are not depicted as rare or expensive. If all it took to wipe out the source of brutal repression was one martyr with one gun, then the entire power structure depicted in the book would immediately collapse.
Even without the fortress shields, this effect could easily be exploited in battle. You could set a lasgun on a trip wire or land mine and take out any shielded soldier. Civilian militias fearing repression could arm themselves with lasguns and shields and vow to attack any army that tried to invade them, destroying them both. This means that a completely untrained levy would suddenly be the equal of the best combat troops in the galaxy, and the source of the emperor's power suddenly disappears.
The sandworms are equally ridiculous. You can't just burrow through desert sand at great speed; the energy requirements to overcome that kind of friction and move such bulk would be immense. There is no way a biological organism in a nutrient-poor environment could manage it. They have a habit of eating both massive factory crawlers and individuals walking across sand. Why do they do this? Are they protecting territory, or gaining nutrition? There is no way that a human body could provide enough calories to make up for the energy required to move that much bulk through the sand. In real life, the only animals that match sandworms in size are whales, and they spend their days gliding lazily through a literal soup of nutritious food. A fantasy novel can get away with creatures like this by invoking magic, but a book that devotes an entire appendix and many plot points to the science of ecology has no excuse.
And then there is the fact that spice from Arrakis is shown to be an absolute requirement for interstallar travel. When it is threatened, the space navigators have no other option and must capitulate to the blackmail. So how did people get around before they found this planet? It is said that there were once many ways of traveling space. What happened to them?
I could go on, but you get the picture. There is just too much hand-waving for this to be taken seriously as a science fiction novel. Herbert should have made it a pure fantasy, set on a single planet with no interstellar travel or advanced science. Then it would have been awesome.