Yeah, it's a pretty problematic film. The biggest problem being Cameron Diaz/Malkina.
It's not just her performance...which is not up to par. Not for her co-stars, and not for the language McCarthy gives her.
But, a real serious flaw of the film is the character of Malkina herself.
This story is, very literally, a cautionary tale. That's an old folklore/fairy tale designed to warn people away from doing bad things. McCarthy even TELLS us this is a cautionary tale in an uncharacteristically on the nose exchange about 'cautionary' diamonds. It's a clunky scene at best.
The basis of the cautionary tale is a story where the protag gets warned multiple times not to do something. He does it anyhow, and everyone pays for the misstep in very terrible ways. Finis. That is this movie in a nutshell.
But, Malkina works outside of these parameters. I'm supposed to buy that she is the evil mastermind behind the events? First of all, I don't. Second, cautionary tales don't have evil masterminds. They have the nebulous forces of evil and wrong doing. The universe punishes you for doing the wrong thing. Everything about the Malkina character in this film screams Hollywood formula in an attempt to make sense of the cautionary tale. And, it rings terribly false. Either remove Malkina entirely or make her a background character who ends up as dead as Penelope Cruz and this film is improved 1000 fold.