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This movie changes a lot from the book, even more than the first one, but I don't mind, since I think they were made with very clear intention; like the first film, I think most of the changes exist to sharpen the book's existing themes for a modern film audience.
The biggest change, by far, is that Jessica and Chani's roles from the book are essentially reversed. In the book, Chani is all-aboard the Muad'dib Train, and Jessica, though she still aids Paul's ascendancy, is far more reluctant and ultimately regretful about the monster she has literally created. Here, Chani is openly hostile to the prophecy, while Jessica goes hard on exploiting it.
On balance, I think this is a change for the better, if not necessarily the one I would have made (and it does introduce a few logical hiccups if you think about some of it). Chani in the books lacks a lot of interiority or internal conflict for how important she is to the story, so having her be a hardline Fremen nativist who smells a rat concerning the prophecy definitely enhances the drama of her and Paul's relationship, and Zendaya carries it off ably. (Chalamet not so much, but I'll get to him). The book wants to be sympathetic to the Fremen, to the way in which they get exploited and co-opted into a tool of galactic politics and psycho-genetic mania, but it muddles it by biasing so heavily towards the viewpoint of the people (mostly Paul and Jessica) doing the exploiting. Since the film mostly doesn't try to capture the book's idea of the Jihad as a primal impulse that even Paul is mostly powerless to stop, I appreciate the decision to instead give the Fremen in general and Chani more specifically a greater voice in the process.
Jessica is somewhat slighted by the change, though; she's much more easily manipulated by Alia, and doesn't seem particularly troubled by unleashing the jihad on the galaxy. I understand how it was necessary in order for the conflict with Chani to make much sense, but I hardly recognize the Jessica from the books, even if Rebecca Ferguson gives a killer performance. I wish they could have given her a little more screen time compared with Chani.
That change ties in with another major one, the introduction of an ethnic subdivision between Northern/Southern Fremen, with Southerners (mostly represented here by Stilgar) inhabiting poorer, even less hospitable regions and believing strongly in the prophecy, and Northerners from nearer Arrakeen being areligious and openly hostile to the prophetic business, which they seem to be aware is a Bene Gesserit sham. I'm not quite sure what is added by this change, other than justifying Chani's skepticism on cultural grounds. It kinda makes the Missionaria Protectiva seem inept, since they apparently failed to indoctrinate the Fremen in the richer, more habitable part of the planet!
I thought the Harkonnen/Giedi Prime aesthetic in the first movie was kinda drab and boring, but here they really go all in on this ghoulish monochrome look, and it worked for me. I do wish the Imperial court had a bit more opulence and grandeur for contrast. The action and battle scenes are very cool, particularly the hand-to-hand combat stuff.
Then there's Paul. I found Chalamet's performance to be adequate, but not much more. In the first film I thought he did a really good job showing an intelligent, sensitive, but also callow and unsure Paul Atreides, but this film required him to project more power and command, and I'm not sure he really stuck the landing. There are a lot of scenes where he plays emotions 'hot' that I would have played 'cold', and much of it comes off like the overcompensation of a teenager rather than the wise, charismatic (albeit still deeply troubled) leader that the story demands him to be. But there are still moments of brilliance in the performance; the weary resignation with which he delivers his final line of the film ("Lead them to paradise") captures well the spirit of Paul's defeated, hopeless interior monologue from the books.
I'm very interested in how they will pull this all together for a hopeful third film based on Dune Messiah; the rift between Paul and Chani that this film ends on certainly introduces complications. Unless they decide to change the plot of the latter books completely, Chani still needs to have Paul's babies, after all.