The highly anticipated 2021 Dune movie dominated the fantasy and sci-fi discussions last year, offering an immersive experience that generally does the book justice. No adaptation is perfect, but, Herbert's Dune has long been considered impossible to adapt due to each unique structure and internal conflict. Taking that into account, the 2021 movie is an entertaining and well-done adaptation, which does, however, leave some big book moments out. In anticipation of the second movie let's consider a few of them.
1) The Banquet in Arrakis
As is often the case with books, Frank Herbert's 1965 novel devotes much more time to exposition and world-building, as well as internal character development that doesn't always translate into visible action. One such case is the banquet Duke Leto holds shortly after the Atreides family arrives to take over Arrakis.
The scene is considered one of the book's best by several fans. It's quite heavy in exposition and serves as Paul's introduction to his world's complex politics. While the banquet would have been interesting from a visual perspective, and it's still important for the novel's world-building, it would work less well on the screen due to the many character motivations that are best understood when their viewpoint is available. The movie chose to skip much of the character's internal monologue, as this would likely be awkward to adapt.
2) Several Scenes About the Harkonnens
Fans of the book or the old cult-classic movie will have noticed that the 2021 adaptation is about Paul, much more than it is about the Harkonnen. Rather than erasing one big moment, the film significantly streamlined the intrigues and the overall time we spend in the Harkonnen court.
The Baron, for instance, had very little dialogue. Director Denis Villeneuve explained this choice, pointing out that this could make Baron Harkonnen more menacing. The director believed that a Baron who doesn't easily reveal his plans at once would be a more menacing figure, and promised that the second film will focus on the Harkonnens more heavily.
3) Paul's Vision
After Paul and his mother, Jessica escape from the Harkonnens and have a calm moment, Paul experiences omniscience for the first time. His vision is still present in the film but a major detail is missing. Apart from seeing the death of his father, as well as many different versions of the future, Paul makes a shocking discovery: Baron Harkonnen is Jessica's unknown father.
This is key information, so we have reason to believe it will be included in the second film. If the sequel indeed focuses on the Harkonnens, being related to them would make the fight against them more personal for Paul, and shocking for the viewers.