The amount of violence, and the nonchalant, depraved, even crazed way it is enacted by the main characters and protagonists, especially towards the end, even though the movie doesn’t show the gory details, is highly disturbing. This should no way have been rated PG-13. Shame on the ratings board for letting this slip through on the “lack of gore” technicality.
Other than that, the movie is just one plot twist after another, never settling into a really cohesive story arc. It felt like it was just going for surprise and shock factor.
I definitely don’t recommend this for kids under 16, and don’t think it warrants even the 3.2 rating it seems to have.