If you are someone like me who hadn't seen the trailers for this or hadn't actually heard of it, and aren't used to films of this type (i.e. British setting based around violence and crime) then you are likely to really thoroughly enjoy this movie. I thought it was one of the greatest British films in a long time, and is up there in my mind with 28 Days/Weeks Later and the like.
The acting is pretty top notch. I thought Danny Dyer and Sean Bean were fantastic unlike a few of the other commenter's, and their dialogue and actions were pretty moving and inspiring. I thought the camera work went well with the type of film it was, and aided in conveying the action, violence and attitude of the movie. There wasn't too much violence nor too little, and at times i was kept on my seat, cringing ready for the next punch, hit with a bat or pipe, or any other act performed.
The ending was pretty cool too and wasn't what i predicted to happen. It left me grinning and i was just really entertained throughout the film.
I think for the people who were looking forward to the film it was bound to not be as good as expected, but if your after something interesting or something different to your typical action or horror flick, and you like British movies, you should really give this a shot. You wont regret it.