Very dull and completely unengaging, such that I couldn't care less about what happened and was glad when it finished.
However, I didn't watch the whole thing. This was a family rental from Amazon. I saw the first hour - in a kind of blank inertia of waiting - then (when the hero had to undergo a repetation of trial by combat) lumbered off into the kitchen, and did chores for about half an hour, then returned to watch up to the end.
I could point at problems with the script, acting, direction, editing, CGI, pacing, preachiness... but when a movie doesn't work, it just doesn't work. Black Panther was the only Marvel superhero movie that I found boring, throughout.
Black Panther was a dud, hence not really fixable.