Attention everyone: The trailers and videos for this "film" tell you exactly what you're going to see. Technically, this isn't even a new "film" persay. As it tells you in the trailer, this is Episode 10 and 11 of the Entertainment District Arc, an introduction to the Upper Rank Demons, then Episode 1 of the Swordsmith Arc. People are leaving 1-Star reviews as if they weren't aware of that going into the theaters. It clearly states what I just said, so please keep that in mind.
With that being said, it provides fans and viewers an opportunity to watch the epic finale episodes of the Entertainment District on the big screen, while also getting a first inside look at the Upper Ranks and the Swordsmith Village Arc. It's not all "new" content like how Mugen Train was a brand new movie that no one had seen, and it tells you that beforehand. That's the way I see it.
As a fan myself, I still think it's awesome to see. I'm not going to complain about watching Demon Slayer theaters. It's still the same top tier animation, epic fighting sequences, and characters that we all know and love, but displayed on the big screen!
People that are leaving a 1-Star review are just silly. Did you not read what it was before you decided to go? It tells you exactly what you're going to get, so don't act surprised and call it a "cash grab." Bottom line: it's Demon Slayer in theaters. Enjoy it while it's here and have a good time!