I think the movie lacks subtext.
I just saw this movie yesterday at a local cinema and found it really... normal.
I didn't dislike it but certainly I wouldn't say it's a masterpiece.
I found some things interesting: I liked how he shot some fight scenes, for example the last one with Sugar Ray was really really good. Or some ideas, like the scene that mixes pictures of the fights and super 8mm's of his life. I also disliked certain things that mostly have to do with DeNiro's acting.
Even in most of my favourite films there are something I dislike, it's difficult for yourself to find a perfect movie. But the great problem I find with this is... there is nothing to tell.
And I'm not refering to story or things happening but to what makes a movie complete: a big idea from the director that is behind every plot point, every shot, every line... This film doesn't have it.
I think most people don't care about this, they tell you a story and it's shot... ok, and you like it. Nowadays in filmmaking that happens a lot you necessarily don't have something to tell but the story.
When the story is judgemental, and ends saying what is right and what's not, even if you haven't something to tell, the story does. But if the story is not judgemental and you haven't got anything to tell this is where it all ends up: a beutifully shot film.
Said that, I enjoyed the film, but I don't think is a great film.