Yes, so there's a lot of violence - so what? I'm personally sick and tired of the gangster-lite presentations of the likes of the Sopranos.
Gangsters kill people - and the more psychotic the gangster, and the more willing they are to slaughter people who get in the way then the more successful they'll become. That's the whole point of this movie.
Some people think that gangsters should be portrayed as having redeeming features - they don't, that's why the Krays never got out of prison alive.
The evocation of 60's London gangsters is particularly good - and cleverly utilises the stylised look of the likes of Performance and Blow Up. Excellent.