I'll tell you what I think happened. I think Ben Affleck watched 'Heat', and thought he'd have a crack at remaking it. In fact, I think he played that bit of Grand Theft Auto 4 that's a bit like Heat, and thought he'd remake that.
The 'Town' in question is Boston's Charlestown, which seems to be one of those places populated by Americans labouring under the misapprehension that they are Irish. It seems that until the 80s, it was dominated by the Irish Mobs, and there's still a hard core of "irish" crims and ne'er-do-wells living there. And it would seem that it's with this community that Ben Affleck's continuing the love-hate relationship he started with Good Will Hunting.
Ben Affleck's the leader of a gang of bank robbers. There's four of them, including Ben, the leader, and Jeremy Renner, the near-obligatory pillock who's apparently only in it for the thrills and violence. During one of their heists, things go a bit pear shaped, and they end up taking the assistant manager, Rebecca Hall, hostage, only to release her once they've made their getaway. They're not sure, however, whether she would be able to ID them, so Ben decides to stalk her a bit, get to know her, and find out what she knows. Jeremy's more into the whole 'kill her' idea. Ben, perhaps inevitably, however, begins to fall in love with her, as much for the better life she represents as anything else.
Meanwhile, John Hamm (Don Draper out of Mad Men, nice to see him in a film role) is an FBI agent trying to work out who Ben and his gang are, and starts leaning on Rebecca to see what she knows.
So, crims are continuing their criminal behaviour, the FBI are closing in on them, Ben's pursuing a relationship that's only going to expedite that, and so obviously, something's going to give sooner or later, and it's all going to come to a head during one last heist which goes a *lot* pear shaped.
In a lot of ways, this is a pretty familiar movie. It's a lot like Heat, and that was hardly original in its day either. So it's not a question of "is this new and original?" so much as "what's Ben Affleck's take on this like?" Well, it's not at all bad. If I have a problem with it, it's that I didn't really feel that Ben Affleck's character had enough good points to redeem his bad points; i.e. that he robs banks. We're meant to feel that he's laudable in some sense because a) he wants out of this life having been born into it, and b) he doesn't personally beat the shit out of anyone, he just brings his mate along who does it for him.
In that sense, he's quite ambiguous, and it's far from clear that he deserves anything other than to serve a lot of time in prison. And in a strange way, it's that ambiguity that elevates it, as you're allowed to go at least some way towards deciding for yourself how you feel about the whole situation. So, overall, I'd say it's a pretty good film, if you're in the mood for it.