Being the "Victor Meldrew" that I am, I always read the worst reviews first, and this film has a lot on this site, mainly by people who didn't like the violence. I'm not too keen on graphic violence either, but in this film it probably has a purpose. Martin Scorsese is a serious, non-exploitive, film maker, so I'm guessing he might have been commenting on the "romancing" of violence by some people.
1. There are parallels in this film to the "Troubles" in Northern Ireland betwen the Catholic "Irish", and the Protestant supporters of the union within the United Kingdom. The Irish rebels are often romanticised by foreigners of Irish extraction, who fund rebel groups. The brutality of the violence in this film demonstrates that there is no romance to fighting.
2. Similarily, gang violence in modern America is also romanticised, and glorified by gangsta rappers. It is made to sound attractive. As this film demonstrates, there is nothing attractive about gang violence.
I found the film very well-made and good looking. It could have been a Ridley Scott film, and I mean that as a compliment.
There were some good performances, especially Daniel Day-Lewis and Cara somebody, who played Hell Cat Maggie, who made Sarah Palin seem like a teddy bear. In addition, Cameron Diaz was far more attractive in this film than she is wiggling her bum in films like she normally does, and her acting was the best I've seen her do.