We all know the story, but in this case Huppert and the director Bolognini make this stand out from the rest. You will probably have strong feelings for Alphonsine, who plays with the bad cards life has given to her, from her pimp father to her ill health. IMDb reviewer Gerald A. DeLuca is right that there is a sort of "didactic" hammering on our main character spitting blood. Quibbles aside, this superb film is just perfect.
Psychoanalytically it also has interesting things to say, like Plessis treating her daughter like yet another man/ suitor at times, or when she goes to live to the rich man's palace, she is given his MOTHER's room (not his own).
Cinematography does help, as does montage (the scene with Alphonsine in ecstasy followed by the slaughterhouse where she drinks blood, for instance). Of course the classical score, based on Verdi's Traviata but also drawing from other sources, heightens the story. All the male characters become supporting ones compared to Huppert, but of course they are excellent. G. M. Volonté in particular. Wait and see.
Don't miss this film! Utterly enjoyable XIX century melodrama!