Unrealistic plot
I think the behaviour of Elena was very odd. I mean ok she might have been insane/obsessed but why then would Jonathan be so stupid to continue the affair and even help her to get her kid in the same school as his?
Also Elena barely knew Grace but tells her with tears in ther eyes that she is so grateful and paints a picture of her. WTF was that about?
Then Jonathan not getting rid of the hammer and so many other wird things.
The soundtrack sounded like chernobyl.