The plot that's there is very simple, and nothing is resolved even in the slightest.
You can argue that it is a "part 1", but then you can look and Fellowship (or even Star Wars, both ep4 and ep1) and they more or less work as stand alone, when they are over you feel like you've been given something of an arc, despite the larger plot remaining unresolved.
DUNC doesn't really do that, it just cuts and and it's "see you in 3 years".
It's so preoccupied with dumping lore on you, that it doesn't even have the time to really explore any of the characters aside from Paul and his mother (and his father, somewhat).
When some of the characters die, you're like "ok, this guy we've seen twice died i guess".
Now compare that to Gandalf's or Boromir's death in Fellowship... hell, even Qui Gon's death felt more impactful, despite that movie being a proper piece of shit.
The political intrigues are quite straightforward, so it's not like they can carry everything on their shoulder.
A lot of time is also spent on Paul's visions of the future that are essentially a trailer for what's to come in future movies, this will likely be terrible for rewatches once those movies actually come out (assuming they do).
But it does feel very grand, larger than life, epic, this is really where it shines, for the most part (some of the costumes i found cheap looking) and why i think the spectacle *is* the selling point.
I'm not gonna call it Villeneuve's weakest, because i haven't seen his super early work, but i do think it's his weakest this side of Polytechnique.
That said, i'm not sure i feel good dumping all the film's problems on him, as i rewatched the infamous Lynch version for comparison lately, and if you isolate the first act, it's basically a 1:1 in terms of plot, and shares similar problems, with a first act that dumps a lot on you, and takes its time, sometimes with really pointless lore details, and then has to rush through the finishline when all the meat comes up.
So maybe the problem is really that first act of DUNE itself, that should be restructured some other way for the cinematic format.