I watched it last night at home, just about as soon after release as I was able. Poorly organized, random thoughts to follow. 
Probably about as good an adaptation as could be done, given the limitations. Unlike the bloated, horrible mess that was the 3-film, “The Hobbit,” I actually think this would have been most properly adapted as a three-film series shot simultaneously, or as a one- or two-season big-budget HBO series a la “Game of Thrones.” There is always stuff that must be excised from a dense novel to get it on-screen, but IMHO too much was missing.
I mostly liked the casting. Chalomet was perhaps a bit too mopey, but that’s minor. I really liked Brolin as Gurney Halleck, and wish he’d had more screen time to flesh out the character. Same with Thufir Hawat; we don’t really get to know him or who he is. Jason Momoa was Jason Momoa, but I think that worked well for Duncan, given that we weren’t going to get deep into his character.
I didn’t like the characterization of Jessica; she spent too much of the film worrying, crying, or otherwise too passive. She was a strong, tough, determined character in the novels, with her own motivations and agenda, and very little of that came to screen. I don’t know the actor, so I’ll assume this is how Jessica was written and directed, and I think it does a great disservice to a very important character.
Costume and set design were largely great. I really liked the Atreides uniforms, except maybe for the armor they wore on arrival to Arrakis. Again, minor. They did a pretty great job of making future technology look well-used and worn where appropriate.
Piter deVries is mostly relegated to “weird-looking dude who is clearly a henchman,” but that’s about all. No Feyd-Rautha Harkonnen at all. There’s still, I think, time to introduce him in the second film, but I wonder if Rabban will sub in for Feyd’s character at the end. It would annoy me, but I can understand why they might do that for story purposes, given all that isn’t in the film.
I wish we had more time in Arakeen to watch Paul growing into the young Duke-to-be, to see Jessica as the Duke’s consort-who-should-have-been-wife, and to develop the more intrigue-heavy plot lines. Yueh’s betrayal had no emotional impact on me at all; it both came out of nowhere and meant nothing, really. A three-film treatment could have ended the first film with Leto’s death and Paul and Jessica’s first escape, giving time for more character development.
I’ll for sure look forward to Part 2, but so far I feel like this film just reinforces the notion that Dune is “unfilmable,” which is unfortunate. I think Villaneuve got a lot right, but had too many constraints.