I agree with blanche-2 and other reviewers, as a former opera student for many years and opera lover and connoisseur.
This may be a delight for those who like Angelina Jolie and like to see a beatiful face on screen, but nothing here resembles the unique quality of divine Maria.
For starters, this is the worse lip-sync I have seen in my life in a biopic of a singer, and it was a surprise that a movie supposed to be a first-rate production went ahead ignoring this major failure. After all, singing is to the essence of the film, it is not a secondary scene. And if you want to recreate Callas life using real recordings, the performative effort must be flawless. Of course it is as hard as demanding, but if you want to compare Jolie's playback what a remarkable, well-executed example, please watch La Mome, the biopic about Edith Piaf, and find delight in Marion Cotillard's perfect, unbelievably good execution. (Jolie's lack of sync is as unbelievable.)
Then, the physique du role. Jolie is one of the most beautiful actresses of our time. But it has physical disparities with Callas which cannot be solved with make-up, and the lack of resemblance spoils the effort. Callas's beauty was tempered, life-chiseled, acquired, a result of a deep effort at self-awareness and self-hardening and reshaping her destiny. That kind of subjective process simply «showed» in her regal attitude, and imposing scenic presence. Jolie is a born beauty, her beauty a gift given from the start, and, in my opinion, she did not manage to convey the dramatic depth of Callas's appeal enough as to create the magical impression that we are seeing a credible Callas.
Also, for those who love opera, Jolie's embouchure (the singers' «mouth mould») is a joke, nothing close to the unmistaken bel canto mouth frame which opera singers (and Callas) distinctively employ. It may seem an unimportant detail, but the sum of inconsistencies and lack of attention to detail ends up being irritating.
I have not listed other observations already pointed by reviewers, which which I concur, related to the use of music score, plot and realism. I really wanted to like the movie, but it was a total disappointment to me.