Crimes of Grindelwald was a great improvement on the first Fantastic Beasts film, with some darker themes, fantastic action sequences, and creative world building. I followed all the subplots of the film and found JK's method of interweaving stories in FB2 familiar - the film seems to handle it similar to how she did in her books.
Critics have bashed the film because it is so unlike what they've seen before. Movies pretty much never have more than 3 stories moving at once, while Fantastic Beasts has like 5 and is setting up for potentially more to be featured in future films. Fantastic Beasts is written like what Harry Potter would be written like in a screenplay if JK had initially written it specifically for film. It's not bad or sloppy - it's different, and it requires an actively engaged, familiar audience in order to be fully appreciated, not critics with a narrow idea of what film should be.
Critics have also said that the film doesn't fully utilize some of its stronger characters. I agree, but I recognize that there simply isn't room, we have three more films, and good stories aren't to be rushed. The misconception that Dumbledore's relationship with Grindelwald isn't acknowledged is outright false.
The weakest parts of the film in my opinion were poorly written interactions between Newt, Tina, Queenie, and Jacob and awkward visual and verbal explanations for magical things that occur throughout the film. Less of the main 4 and more of everyone else in the story would be great. Also, sometimes connections and symbolic moments are better left unexplained for the viewer to discover.
Credence continues to feel like such a bizarre and out of place character (I feel he is given undue importance in this series, and the character feels jarringly one-dimensional), but he became a little more interesting thanks to Leta and other supporting cast in this film. I'm with the crowd that theorizes Grindelwald may be lying to him about his family. Contradicting canon by making McGonagall a professor before she was born was saddening because it breaks the worlds internal believability whenever it isn't self-consistent, even if inconsistencies found are small.
Keep up the writing JK - I look forward to the rest of the series! Please don't dumb it down for a wider audience - pursue your vision and your audience will follow.