Having seen the SyFy miniseries, I refuse to believe that Dune is unadaptable because it was possible in the early 2000s. It might not look visually stunning and the costumes look goofy but the character work is staggering and the writers go out of their way to give minor characters like Irulan something to do so that her character has a chance to shine. It does all this in less time than Dune 1 & 2 combined.
I came away from Dune 1 largely hollow towards the characters because it felt like they weren't all the way there. Oscar Isaac is a good choice for Leto but we so little of him that his character isn't there. Several of Dune's key points were removed and the film suffers because information is lacking further backing.
The importance of water isn't emphasised as much and as a consequence, Liet Kynes is non-existent. Kynes's dream is important because Paul manipulates it to control the Fremen. There's supposed to be a dinner scene where a lot of the power plays going on in the Empire are presented. It's also where Paul begins to play the political game himself. It's where Jessica's character has a stage where you can see what she's capable of. Not having this scene removed context for the politics in Dune's world.
After seeing Dune 2, I enjoyed it a lot more but it confirmed for me that the movies are all spectacle and no substance. I didn't care what was going on, it all just felt like it wasn't Dune, I didn't know these characters. I hated Stilgar, he was incredibly annoying throughout the movie. I have no idea what they're planning to do with Chani. She has a part to play in Messiah which requires certain things and I don't think we're getting them.
I would say the acting is pretty good. Especially Alec Newman playing Paul. The weakest one I always thought was the actress playing Chani but she gets better in Children of Dune.
The cast is strong in Denis's version for sure. I was uncertain about Chalomet for Part 2 but he did well. For me, the cast could've shone so much more if the character work was better.