In a nutshell: 'When the Harry Potter franchise catches the same disease that lead to Peter Jackson's Hobbit Trilogy.'
The movie is solid, mostly because the actors carrying it all do a Fantastic (Pun intended) job. Johny Depp steals the show, and whenever he is on screen the movie picks up significantly. I am really glad that Rowling ignored the ludicrous allegations and went with Depp as Grindelwald.
This movie's Achilleas heel though is its monstrous editing. There are scenes that are plastered together in a way that makes no chronological sense, and landscape changes are almost always wonky, leaving you with a few seconds of asking yourself: 'wait did they apparate, fly, time jump, light speed travel here?'
The other major issue is pacing. The movie tries to set up a dramatic conflict, but because it needs to pad time for the inevitable sequel, the pacing fails to make anyone really care for the conflict until the very end, when Depp finally gets to properly come out to play.
Overall: Worth seeing, but keep your hopes down. It won't leave you breathless like all other HP Movies have in the past.