Mary Harron: wtf

I re-watched this movie a couple weeks ago and hadn't seen it for a couple of years— I'm shocked by how shoddy it was, and sort of angry because it could have been an amazing movie had it been done right, or even slightly well. Mary Harron is not a bad director, so what went wrong here? Awful pacing, terrible script and dialogue, bad acting... seriously, what happened to her with this flick?