I think some people went in with the wrong expectations — it was a $50M A24 movie about war photographers, not a $250M Russo Bros or Roland Emmerich movie. It was never going to be a narrative about the Civil War itself.
I thought Kirsten Dunst was good, and it had lots of great scenes, but it never really coalesced into anything meaningful for me. Ending with the president was dumb and made no sense.
Worth a watch but not worth going out of your way to see IMO.