The easiest way to talk about the movie is the story. The Fantastic Beasts series is a backdrop for the first wizard war alluded to in the original Harry Potter saga. Instead of making that the focus, J.K. Rowling decided that pretending the series is about magic animals was a good idea. So the movie splits its attention with animals, love stories, queerbaiting, and war, doing none of them justice. Plus, in an attempt to bring back fans, this movie has included characters from the original set of stories that are extraneous and add nothing.
One moment you are with the characters from the first movie, then you jump to Grindelwald for ten seconds, but don't forget a flashback that isn't needed, ending on new characters that aren't important. The movie wants to be taken seriously, trying to have moments that will take your breath away while also being a character drama. This falls flat because the magical moments are mundane, not really eliciting any childlike wonder. The serious moments miss the mark as well, due to the characters' actions not being indicative of their motivations. In addition to these hindrances, you have the story being too circumstantial. It felt like someone saying, "You know what would be cool", and not having a plan for it.
I guess negative reviews won't keep people away though, as the rotten tomato score has proved. Some might argue that the story is all planned out, that I just need to have faith in the three movies to come. I would shoot back with, that is never the case; things change, and that is not how movies work. This isn't television, books, or any other serialized content, this is movies. Being a movie means you tell a story, and The Crimes of Grindelwald failed in telling a compelling one.
The actors do a fine job acting, its just all the creative people's fault this movie is bad