Poor Ending (spoilers)
Unlike a lot of the comments here, I really enjoyed the movie. And I didn't find the kids to be that bratty. And I thought the relationship between the 2 brothers was very realistic.
However, like a lot of movies these days, the ending was a huge let down. I guess there's a trend where the executives think leaving the ending "open-ended" and leaving the audience hanging is just being artsy, but really it's just a lazy way to end and disrespectful to the audience who just spend 2 hours watching.
In this particular movie, I think the father should have definitely killed Brad (the oldest boy). It would have been a much better ending if he had killed Brad, let Caleb go because he at least showed some effort in bonding with the dad, and then kill himself.