First off, I can understand why some people would not see this as a good film. As a stand-alone film, it is terrible. You cannot take it on its own value, half of the references are based on what we learn from the earlier two movies. And it is definitely a between movie, much like Two Towers was a between movie in the LOTR saga. So, if you have not seen the first two films, "Fantastic Beasts and Where to Find Them" and "The Crimes of Grindelwald", do not see this film until you have seen the first two in order. You will definitely not be able to catch half of the references.
In fact, I advise you look at the first two movies anyway before seeing this film.
Now, that said, this film is absolutely GREAT! As a bridge film between the first part and the upcoming last part, it perfectly fits. It continues the plot laid down by Beasts and continued by Grindelwald. The surprises, some of which are unexpected, are absolutely satisfying. It keeps you on your seat from the start to the end. And the end is quite satisfying.
Only thing is, I was sorry to see Johnny Depp was no longer playing Grindelwald. But Mads Mirleksen did a fantastic job of replacing him. So, I am on the fence with this one - on the one hand I like Depp, on the other hand I like Mads. A toss-up as far as I am concerned. But a good one. Mads take on Grindelwald is quite unmistakable. If anything, it makes Grindelwald a bit more ... dangerous.