Overall I found it a decent film, but the pacing and the twist aren't really that well executed in my opinion.
The first act takes a bit long to really build anything up, and there's some stuff that could've easily been cut a bit shorter to tighten the cut a little bit, since the film often feels much longer than it actually does by spending too much time with some of the material, though this mainly applies to the first act. If the movie had worked up some better pacing from the beginning I think it would've been a bit easier to process as a whole.
I didn't really have a lot of problems with the second act. The pacing seemed to speed up a bit, and the sense of tension and dread was pretty well executed. Rooney Mara's performance in particular really helped film quite a bit, and the switch to Banks as the main protagonist was pretty interesting.
The twist however kind of brought the film down, especially since it kind of revealed too much prematurely in my opinion. There was something a little hollow about Catherine Zeta-Jones' character that seemed a bit transparent to me, and it was pretty easy to guess she was involved in some manner even before it was all revealed.
In the end I don't really think Zeta-Jones' character was really needed aside from her initial appearance concerning her past with Emily, and I think she could've pulled it off by herself, which would create for a much more compelling third act had they also made the buildup to the reveal a bit more tense.
I did like how Law's character provided both a protagonist and antagonist for the story, which really puts the ending in perspective because he took the law in his own hands. Emily definitely deserved to be punished, but it wasn't his call.