1. The plot was moving too quickly and without enough context. She said she didn't understand much, and I can relate to that. If I haven't read the book I wouldn't be able to pick up with the plotline.
2. We didn't have any feelings towards any of the characters. We weren't sorry for Leto, we didn't identify with Paul, Jessica or any other character, we weren't even hating the Harkonnen.
All this led us to the conclusion that it was better to take things more slowly, investing more building the characters and context and getting people "onboard". This would have probably required to split the book into 3 films instead of 2, but I think it would have been worth it.
Edit: On DDG, search "dune miniseries <file-extension>", the second result has a working magnet link.
Two good examples are the pain box and the slow blade penetrate the shield in training.
While the new Dune movie mention how they work - they just do a bad job of communicating that as effectively as the 1984 movie. To really appreciate this movie, you either needed to have read the book, or watched the prior movie (1984), or the TV mini-series'.
They also introduced things from the book, like how to walk in sand, and the visions of the jihad, but describe them poorly, and leave the viewer wondering why they're even mentioned. It's just badly written.
...but there were other issues with the movie as well. Long useless sequences of sand visuals that added nothing to the story - and that annoying scream sound that left our eardrums ringing, for no other purpose than to try to make the audience feel like an uneventful scene is somehow important to the plot.
A lot of people complained about the voice-overs in the 1984 film but they actually added a lot of value by efficiently introducing concepts to the viewer succinctly - especially the intro in the beginning which sets up the universe.
The best take on this universe after the book is actually SciFi channel mini-series in 2000 and then the Children of Dune in 2008.
All that you say can be true, each of those changes likely would make things more informative - but doesn't mean they necessarily should be added.
"SooOooo I wasn't excited to see this movie. I think I might have seen the old one, but I don't remember liking it. This movie though was amazing and now I'm just mad I have to wait two years to see the sequel!"