You spoke my mind. I just finished my first screening and sharing my initial thoughts. Disclaimer: I have not read the book.

I really liked the slow pacing of part one, it gave me time to really appreciate the cinematography, it's characters, and the music. This part was paced much quicker, so with me looking forward to "step into Arrakis" again, I left the cinema felling a bit disappointed. I felt that this could have been split into two 2 hour or 2.5 hour movies to flesh out some story bits and the characters. So many new faces, so many potential stories, so little time. It felt like Paul just went to the south for 10 minutes to get his drink, and then we're back north again. I wonder if the book is also paced like that.
Soundtrack was another that got let down by the fast story pace imo. Not to say that it's bad now that I'm listening to the album on Spotify, but the slow burn combination of visuals and sound in part one left such a great impact on me, part two just felt like it passed a bit too quick.

That being said, the bits where they want you to appreciate the cinematography, they let you know and execute it really well. I really appreciate the black and white tone of Giedi Prime, how they portray the cruelty of the Harkonnens, the sandworm scene, the scale. I would still highly recommend a watch, and I plan to watch it a second time (and maybe third). Maybe I'll have different thoughts and learn to like it more after that.