When i read the storyline, i found it really interesting, although not very original. And most of the movie is really good, but i think the story should have been more developed. The first part of the movie shows a bit of the characters and then their little trip to the river and the development of their plan. But the movie ends just when it starts to get interesting. They should have explored more the different reactions to the accident and the tension between the characters.
But i still think the movie is worth watching because it shows how everyone has diferent sides and it makes you dislike but also feel sorry for the same character at different moments.