Second thoughts after another viewing:
The movie is roughly 2.5 hours long.
The first 1.5 hours is still more-or-less what I've said in my previous comment. It's a lot of set up and world-building (which is good) while also being a bit dry in terms of getting to the actual story.
The last 45 minutes or so starts to get into telling a rather good story. Then it's over.
The choice of place to stop makes sense.
Thinking back on it all, my opinion is that a large chunk of this movie feels a bit like a prologue. It's a necessary prologue to understand the stage upon which the story takes place and to understand who the characters are and why they're there, but it's not always an enjoyable ride to sit through. I wouldn't say it's bad; but a few parts are (as said) a bit dry. It's occasionally rough to sit through in the same way that Season 1 of Game of Thrones was necessary to set the stage but had episodes which were dry until the ball got rolling.
Once the movie gets to the actual story, I think it's an enjoyable ride, but one which ends quickly. In some ways that's a good thing because it stops at a point where you're left wanting to see more. On the other hand, I believe that how the entire story is ultimately viewed will depend upon how much time the audience is required to wait before seeing the next part.
Most of the cast seems fine when the actors are actually acting and not just kinda standing around.
Dave Bautista seemed fine for the part for which he was chosen. It'll be hard to judge before seeing the next part. Still, I think his acting has improved over the past few years. He seems to be putting effort into his craft.
Jason Momoa wasn't great. I don't expect a wide range from him. Though, even without high expectations, it was one of his weaker performances. I was bummed by that because I actually like some of the work he's done in other shows and movies. Here, it just didn't seem as though he was putting in his best effort.
I enjoyed the movie enough to want to see more. Simultaneously, I still think that a portion of the movie will be a bumpy experience for those unfamiliar with the source material.