These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Darkness-Induced Audience Apathy: On the one hand, Nick wants to protect his wife and remaining son from Billy and his gang of killers. On the other hand, he made himself out to be as bad as the killers themselves. Therefore, it can be hard to root for him.
Billy and his gang of killers crosses this when one of their members kills Nick's son, Brendan, at the gas station hold-up. And if that wasn't enough, they raid Nick's house later on in the film, with the leader himself fatally shooting Helen, the former's wife.
Nick himself also crossed the line after he killed Billy and the rest of the gang at the end, which goes to show that they're Not So Different.
Narm: The cartoonish violence of the climax can really undercut all the dramatic stakes the movie had built up to that point.
One-Scene Wonder: John Goodman as Bones Darley, not in the film much but he owns the role he's given.
They Changed It, Now It Sucks: Averted. Author Brian Garfield loved the movie adaptation and how it makes the same point about revenge he was trying to make in the novel.
Unintentionally Unsympathetic: It's hard to sympathize with Nick by the end of the movie, considering that it's his fault that he put his family in danger in the first place. Which is the message of the movie; vigilantism isn't all it's cracked up to be.