There are countless reviews of this movie and there seem to be some consistent themes that I feel really hurt the potential here.
1) Too many storylines going at once that had no necessary intersection with each other. Searching for magical creatures to create a zoo-in-a-case is its own story; Grindelwald and the Obscurial is its own story. Each of these could have happened without any need for the other.
2) Actor choices could have been improved. I could not understand or hear many of the lines delivered by the primary actor because they were mumbled. The director should have fixed this and redone the scenes. Also I don't enjoy actors who point their head's toward the ground while they are acting. It constricts the throat, we can't hear what they are saying, and we can't see their mouths move to try and decipher what they are saying. It also gets tiresome looking at someone looking at the ground.
3) So much potential with the Obscurial and we got almost zero information about how it happens, why it happens, why it happened to this character, etc. It's briefly mentioned that it's when someone tries to hold back their magical powers or suppresses them, but based on the destructive force we saw in this movie the Obscurial is more powerful than Voldemort or Dumbledore or anything we saw in the HP movies, and it should have been a MUCH bigger deal.
4) Exposition - I am not a fond fan of the sweeping monologues that are overly dramatic and don't move the storyline forward. The ending when Grindelwald in disguise is on the train platform lecturing...get on with it!
5) Get on with it! In general! The movie was an hour too long...I'm not even sure that anything of relevance happened within the first hour of the movie other than setting up the third storyline that I didn't even mention yet and that's the love story with the mind reader and the muggle. Third movie right there - or at least a short story.
The movie suffered from lack of an editorial eye on the script, and lack of a directorial eye on the implementation.
It is unlikely that I will watch the sequel given how rough the first was. It's sad really - because it held absolutely nothing of the magic and adventure that we saw from the Harry Potter adaptations.