First off, I gotta write down "pointlessly nihilistic" somewhere. It's perfect.
Second of all, I agree with all your points, though I'd argue the movie has even less respect for the mentally ill than it does for women. But "dreary and nihilistic" is kind of the point. If you felt the movie was "dreary and nihilistic"... You've watched the movie.
I'm not saying the experience is an enjoyable one, but that was the point. It's a feature-length feel-bad film. It opens on a horrific mass-killing and you spend a good amount of time trying to parse what happened and what it means. It doesn't want you to enjoy it. And if you're okay with that, it's a well-shot movie that knows how to pull the rug from under you.