The reviews said it would be better.

Rating: 5/10 (31 October 2009)

This film had some exciting moments and a good premise. But in the end, It seemed to start off high concept: prisoner holds all the cards. But Butler's character dissolves into a monster not unlike Darby, the guy who killed his wife and kid.
First of all, why did the Assist. DA, Foxx, take Darby's testimony to hang Ames? Darby was the doer and Ames the tag along. That's a game changing mistake right there. If the Foxx character had done it the reverse way Butler's character wouldn't have been so justifiably worked up; the true killer would have gotten the joy juice. You can't tell me Ames was too loyal to turn states evidence. So the whole movie needs a ridiculous set of facts to be set in motion.
But accepting that for arguments sake, the movie presents a promising scenario -- a man who is so good at taking the law into his own hands that he can call the shots. But then the movie turns crazy. Why does Butler shun bail? So he can wage war on the city justice department? OK, but he could have done that easier on the outside. True, doing it from the outside wouldn't have made Foxx's character look so idiotic but it would have made Butler more believable, less reckless and out of control. Instead he starts to kill innocent people from within, like his cell-mate and Foxx's assistants. It is now a lot harder to like this guy. He's mostly on a power trip--one designed to rub everyone's faces in their own sh*t. What high moral principle does that champion? After many more deaths of people who only vaguely helped to execute the wrong guy, Butler hears Foxx's last appeal for reason. The audience is mostly seeing it his way, i.e. enough is enough. But Butler can't get out of his own obsessive sickness. So killing him was more or less logical. Butler had morphed into a pitiful joke compared to his original goals. Did the movie really want us to jump back onto Foxx's side? I wasn't comfortable with that. I felt disappointed. There was no real point to the film then.
I'll take Dexter over this guy any day. Dex never takes out the innocents. And his code only covers true destroyers of life who have no chance of ever rehabbing. And he does it all anonymously--the vigilante lives to fight another day.
Afterword: I've been a bit dishonest here. I was actually rooting for the Butler character to blow up city hall. I guess it was the logic of the film that I'd bought into. Now I see that there are two sides to me--a peaceful citizen and an enraged maniac. I disowned the maniac the minute the movie ended.