The best thing about this movie is the atmosphere. It does a great job of taking you to New York 1863. I'm no history buff, so have no idea how accurate it is, but the setting is great and there are some truly great shots in this movie. Bill the Butcher is an exceptionally memorable character as the extreme patriotist, played very well by Day-Lewis. The rest of the cast is just ordinary.

There are two reasons why I didn't like this movie. 1: there is only negativity; in the dark setting, the unlikeable 'hero', the motives of the characters (hate and fear), the fighting all the time, the sad ending, everything. 2: there is no character development, they all stay exactly the same throughout the entire film.
It can be said that these two point were done intentionally by the director, to make people walk away with the sad, empty feeling that bad things will never change, but in my opinion it missed something to make me care about. Now I just shrugged my shoulders and moved on.