Finally saw this last night (thank you Netflix).
Wow. DeNiro was incredible.
I found it to have a lot of disjointed storytelling like most of Marty's early films had. You had to really listen and watch closely, and it seemed like there was more action than dialogue so you had to do a lot of mental "connect the dots" (for last of a better explanation). A lot of his early work feels that way to me. Somewhat disjointed, like a bunch of spliced together scenes.
But I have to say that all in all, DeNiro was incredible. Did he actually put on a ton of weight for the role for those later scenes, or was that makeup? It looked so realistic, and he was so convincing. I think it was DeNiro's best role ever.