THIS REVIEW HAS SPOILERS, READER YOU HAVE BEEN WARNED.
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Crimes of Grindelwald wasn't trash, per se, but for someone who's been a Potterhead for a long, long time (such as myself), it's hard to digest the numerous plotholes and still love it like I loved the original Potter movies. There were a lot of things I liked about the movie (French MOM, cemetery scene with the blue fire, the Newt-Theseus dynamic, just Jacob in general, to name a few), but there were also a lot of things that threw me off (Dumbledore teaches Transfiguration, not DADA; McGonagall is actually younger than Tom Riddle, there was no way she would've been there; Nagini's presence didn't add anything to the plot other than she was Credence's companion; freaking AURELIUS like where tf did that come from), and these details may seem small to the average viewer, but it made all the difference for me, someone who enjoyed the first film and watched it over and over again.
Overall, Crimes of Grindelwald is good for a surface watch, if you really want to see something related to HP and aren't too fussed about the details, but hardcore Potterheads will find this disappointing and lacking where the plot is concerned (and that's a hard thing to say, especially since J. K. Rowling herself was involved with the material put on film, much more than she was with the original HP films).