How would you rate movie adaptation of Dune compared to LOTR?
No comparison. The LOTR movie is way above Dune. The good thing about the LOTR movie (I haven't read the books) is that the pacing is just right and all characters are well established and story events progress in a way that makes sense.
I don't have an issue with movies changing the narrative from the books. The issue I have with Dune is in it's implementation. The pacing is a bit too fast, as in events occur before main characters are properly established. For example, we don't know much about Rabban and Baron Harkonnen other than them being evil and that they hate the Atreides. So, the only thing we can infer is that they attack Arakeen simply to destroy the Atreides bloodline. I don't think this is a strong enough motivation. In the book,
the Baron Harkonnen has an elaborate plan on not only destroying the Atreides, but also to put his nephew, how is not mentioned in the movie, on the throne as a new Emperor, in fact he's been grooming his nephew for exactly this for most of the book.
Similarly, when the Sardaukar are introduced, it's in a scene that makes no sense and tells nothing about what they are capable of or what their motivations are. Literally no difference between the Harkonnen troops and them.
How the spacing guild "folds space-time" to travel faster than light is also not shown. One moment they are on Caladan and in another scene they are exiting the guild ship to land on Arrakis. Imagine not showing how ships travel in hyperspace in Star Wars.
Now, all of this makes sense in the way that the movie is mostly focusing on Paul while the books told the story from the point of view of other characters as well. But still it makes important characters such as the Baron and other bad guys just two-dimensional cardboard cutouts. Plus I think some more details should have been shown.
I could rant more, but this post has already gone way off-topic.