I think you had way too many expectations about this film. It is about a superhero take on the Norse myths. Who told you it was supposed to be an accurate representation of the legends? The previous films including Thor should be a hint to what directions the film would not take.
As for Cowboy Beebop-it it a series. The writers have time to fully flesh out a character in detail. Movies like this generally don't and you have to take into account that not everyone is familiar with Norse legend. That said this is a super hero action movie, not a retelling of the myth. The movies goal is to tell an entertaining story and make a profit.
I personally think the movie was used as a lesson of you can't run from your past, eventually you have to face it. And that is what happens. Odin's past comes back to haunt everyone.
Stylistically, all the sets have a purpose and express that purpose, from the roof murals to the catacombs. Odin tried to cover up and bury his past...it didn't work.
The studio made a movie about facing the past and meeting a new future...in average movie screening time.
If I want an accurate depiction of Norse mythology, i will reread the legends.
RE: Thor: Ragnarok and the Rejection of Myth