Before diving into what people have already been discussing, I want to remark on certain changes, at least the ones I could recall.
The most notable change that stood out to me was Ilia's role and I quite liked the decision to have her still in utero, telepathically communicating with Jessica. I've never seen something like that before so that aspect really appealed to me (even though I'm sure it has been done before somewhere across film, television, and novel). Of course, this meant changing who killed the Baron and, while it's a shame we didn't get a creepy child as the assassin, Paul's confrontation was nonetheless effective.
I do wish Anya Taylor-Joy's appearance in the film hadn't been leaked (regardless of her presence at the world premiere) because that would've been one hell of a surprise reveal during Paul's vision. I didn't recognize her voice during the communications so that facial reveal would've properly floored me. Without having read
Messiah, I'm curious to see if we'll see a big time jump (and how such a jump would effect the overall plot) for the third film to allow Taylor-Joy to continue to play the role. On the other hand, that'll look weird alongside people like Timothée Chalamet and Zendaya when she's a few months younger than the former and a few months older than the latter.
Even though I just reread the novel just a few years ago in preparation for the first film, my memory sucks so I was blurry on some of the other changes, particularly regarding the immediacy of the conflict with the Great Houses and Chani's open rebellion against Paul at the end. I was fairly certain both didn't occur in the first novel but I couldn't remember exactly how they did play out. Until this morning, I was blurry on the Fenrigs because I can't even remember if Lady Fenrig seduced Feyd or not in the novel while I was watching the film, but now I do recall the role she played in the novel.
What i really loved was how focused Villeneuve was on the religious fundamentalism core of Herbert's work and the massive force it can exert on people's lives, it came through well in the movie in the figure of Stilgar. Starting out as a proud leader of his people, independent and powerful but little by little consumed by his faith until he became a fundamentalist.
I loved that focus, too, especially since I worried that theme would be lost in translation for general audiences. Hell, some readers of the book miss that point, so it's good that Villeneuve made that theme very clear here.
What I really miss from the '84 version is the casting and the music. The latter practically deserves a thread of its own. Sian Phillips as Mohiam will never be topped in any movie iteration of Dune, or Francesca Anna as Jessica.
While I respect your opinion on that, I have to disagree. I was blown away by Charlotte Rampling's depiction of Mohaim's nastiness and I say this as a big fan of Phillips thanks to
I, Claudius. I also loved everything Rebecca Ferguson did as Jessica. I will say this comes with the caveat that I've only seen the Lynch version a couple of times and don't have any strong loyalty or nostalgia towards it.
How are people feeling about the decision to make us all outsiders watching Paul, and not seeing his visions at all post water of life/hardly at all pre?
I thought it was a unique perspective, that also allows an additional level of ambiguity over what is happening.
Again, another choice I personally would not have made, but one that works well for this movie.
Honestly, I was disappointed by the lack of visions (aside from the one centered around Alia) but I get why that perspective was chosen. Less is more is an effective tool, but so is show not tell. I'm ultimately torn on this decision. I'll see how I feel on repeat viewings.
I read last night on Wikipedia about both of those characters being omitted.
I had just figured Thufir hadn't been included at all (especially considering his main arc was omitted in the first part and the importance of the Mentats wasn't explored) so I was a little surprised to learn Stephen McKinley Henderson actually filmed scenes that were ultimately cut.
It's curious Tim Blake Nelson has chosen to remain mum who he played (but I respect his deferring to Villeneuve on the manner), which makes me wonder who he played. Aside from Count Fenrig (whose omission is no great loss in my mind), I can't think anyone of significance who was missing. Considering we didn't see Lady Fenrig during the conclusion, it would've been hard to cut the count, too, unless they were conveniently off to the side. My only other guess is a character introduced in
Messiah that Villeneuve decided to introduce early but then cut for time, which is why Nelson has chosen to remain mum.