This film is not a happy film, and not knowing anything about it I wished I hadn't picked it as it bummed me out. I go the cinema to escape to a happy or silly place. Not a bleak hole like this. It's very similar in mood to Requiem for a Dream or Taxi Driver.
Joaquin Phoenix is very good in this. The violence is mostly off screen and the story (he rescues girls from paedophile rings) isn't Disney. It'll get good reviews for the performances but the stand out for me was the soundtrack, which is great.