This film is intriguing in that it describes how i (think, at least) would feel if someone were to hurt someone in my family and "got away with it".
These are real life circumstances, and the acting is plausible in that these are everyday characters. We see them all the time in our daily lives, and shake our heads or applaud their behavior as we assess what we feel are their shortcomings or positive qualities. To dismiss this acting is to be simply out of touch.
Is it a great movie? Not in my opinion, but it embodies a realism and a sense of seeking justice in a society where we often fail to find any. In the wake of the great push by corporate America and our paid for politicians to strip away opportunities (in other countries as well) this movie helps to claw back a bit of the essence of our own lives, and provide at least a glimpse of hope. These feelings are palpable; this film is not about entertaining with fast action, glitzy cars and shimmering flesh; it wants us to feel something deeper.
Do you have to lose someone to identify with the themes here? Grieving people and those around them often *are* wooden when facing such losses. Seems to me that a 'good' movie like this can help you to understand. When we feel this helpless - this is a good mirror.