Mixed Bag *Spoilers*
I love the HP films and books and I enjoyed Fantastic Beasts, but this was a mixed bag imo.
I found the plot hard to follow often and I thought it diminished the complexity of characters such as Dumbledore and Grindelwald. Other characters made some strange decisions such as Queenie and Newt. Why was it so hard for Newt to pick a side? GW was killing loads of people and is a Nazi, but it takes someone close to Newt to die for him to change his mind? Credence is still a confusing character and the twist at the end just felt like a cop out to conclude on a giant cliffhanger and to get people to come to the next one.
GW is basically portrayed the same way as Voldemort. His character and motives aren't fleshed out at all; he is just evil and a villain. Also, DD, in HP, is hinted as having a romantic past with GW. Instead of having DD avoid fighting GW due to a conflicted emotional reason and exploring that, we get he can't because of a magical bloodpact and the same reason as to why GW can't face DD. It just seems unimaginative.
Overall, I thought it was an OK film. The effects and creativity surrounding the beasts were outstanding, but I thought the plot, character motives and decisions, and execution of the film could have been so much better.