Harry Potter was a tale well told, and introduced a rich, colourful world with an internal logic that more or less held up - and could be transferred to the big screen more or less successfully. As the series progressed, the film makers found themselves including more and more extraneous details as nods to the source material rather than concentrating on the main thrust of the storyline. As such the final 3 films 'worked' but without any prior Harry Potter knowledge could easily have buckled under the weight of "huh? What's THAT?"
JK Rowling's two screenplays in this new franchise suffer further in that there is no source material at all beyond the script - so all the world-building is being done on screen in front of us. Hence characters are endless explaining the tortuous plot to each other for 2.5 hours (explaining the otherwise entirely useless appearance of Jacob Kowalski). Throw into the mix the increasingly tired "you though this guy was this.. but actually he's THIS!" device and it's increasingly hard to believe in or care about any of these characters.
Unless Rowling steps back and becomes a curator of the overall story - handing screenwriting duties to someone with a track record in the medium - this franchise will be lucky to get past a third installment.
Amongst the dross, Jude Law is outstanding - the only character with any sense of fun in a series which, ostensibly at least, is aimed at children.