If you haven’t read the manga or watched the anime series, I HIGHLY recommend that you do at least one of them before going to watch the movie. It would make a lot more sense and build up your anticipation after the ending scene.
I somewhat agree with the confusion of the Upper Rank Demon’s random appearance. There should’ve been a small forewarning somewhere that he would appear.
Overall the movie is a must see, some scenes dragged on a little more than others but if you’re into heartfelt scenes you will love it. It was a great idea to make it as a movie rather than break it up into eps. Could’ve went a little harder on the fight scene between the Hashira and U/Rand Demon, but it was still pretty sick.