The ending of Dune (2021) shows Paul and Jessica being accepted by Stilgar's Fremen after Paul wins a duel with Jamis, and Paul then decides to join the Fremen and fight to take back the planet. Spoilers follow.
What does the last scene actually settle? Very little about the war, and quite a lot about Paul. The duel matters because it moves him from a hunted heir to a member of the Fremen, which is the outcome his dreams of Chani had pointed toward from the first act. When Chani says that their fight is just starting, the film is saying that the story is a first half, and it does not pretend otherwise.
The sequel picks up that thread. Dune: Part Two opens with House Atreides destroyed, with Paul and his pregnant mother Jessica sheltering with the Fremen at Sietch Tabr, and with the Baron sending his nephew Feyd-Rautha to take control of the planet. So, the ending is best read as a handover, not a conclusion.
In my opinion, this is the right call for the story being told, although it could be argued that viewers who expect a self contained film will find it abrupt. Perhaps the simplest advice is to watch it with Dune: Part Two within reach.
Why is Dune 2021 so good? In my opinion, the answer lies in how much of the film feels physical: Greig Fraser's IMAX photography of the Jordan and Abu Dhabi dunes, Hans Zimmer's score, and a sound design built partly from real shifting sand recorded in Death Valley. That being said, taste varies, and the deliberate pace is where opinions tend to split. For the book comparison, see Dune books vs movies.
