This is not a bad version of the stage show. It follows the original book of the show pretty faithfully, albeit with some padding.
Anyone who has seen Wicked on stage will remember Defying Gravity as an exhilarating moment. It's presentation in the film, for me, dilutes the power of the song. The songs, particularly Defying Gravity, were written with the traditional Broadway Belter in mind. As good a singer as she is, that is not Cynthia Erivo's style. The songs have been rearranged slightly to better fit her but that does, for me, weaken their effect in some important moments.
Cynthia Erivo is fine as Elphaba but I was genuinely shocked by just how good Ariana Grande was as Glinda. I really hadn't expected that.
No doubt far more people will love the movie than have reservations. Having seen some spectacular casts on stage, I fall into the latter category.