This is a fantastic film, and I'm going to tell you why I think so, and by the time you finish reading this, you just might change your mind about it, or run out and have to see it.
The music is great. Perfectly fits the time period and setting, I dunno how much they had to pay in royalties for the songs in this film, but I love em'.
The camera work is fantastic. There's a scene where the camera gives you charlie's viewpoint, stumbling, wobbling across the bar, lights flashing, people dancing, music blaring, then zooms out to his smiling happy face. Then there's the filming of the street festival and the overall way which New York is captured so perfectly. It feels like you are really in the city, the movie has that gritty feeling to it.
The dialogue is great, many of it is ad libed by Deniro and Keitel. This is the beginning of ad libbed dialogue for deniro, the culmination being his speech in front of the mirror in taxi driver; "You talkin' to me"? There's a scene where Keitel confronts Deniro outside the bar to ask him about his debt, the exchange is perfect, it could never have been written and its executed beautifully.
The acting is also fantastic throughout.
So, great acting, great filmwork and great dialogue all come together to create a wonderfully realistic film.
Now, the end of the movie, maybe you didn't understand it, so I'll explain the film. I'll try not to spoil the ending.
Ok, so Charlie does some bad things, he works for the mob after all, and he wants to repent for his sins, so, after going to church and then later seeing jonny boy in a bar he thinks that God has asked him to repent for his sins on the streets, by helping out Jonny Boy. He doesn't believe that saying a few hail mary's or confessing washes away one's sins.