As it says in the book, this film is the missing link between American Film Noir and Italian Neo-Realism. The argument should go that Ossessione is what Rome Open City gets credit for, the first of the Italian Neo-Realist films. It didn’t get that credit because the Fascists obviously kept it out of the light of day in addition to American copyright competitors who kept it out until 1976. This film is truly taking the techniques and inclinations of the French realistic directors of the 30’s, notably Jean Vigo and Jean Renoir, and brings it to Italy, creating as we all know, the Italian Neo-Realist movement, which in turn as we all know, moves back to France in the form of the French New Wave.
WW2 changed much about film, but definitively it brought realism and the attempt for it to the forefront in cinema. It also altered the psyche of protagonists after it due to the moral complexity of the war. The great pressure cooker of WW2 fundamentally altered reality and thus the stories became darker and the heroes look a lot more like villains. The tradition for realism before this time was apparent in French and foreign films whereas the advent of talkies brought about the opposite sensationalist, escapist, genre based film system in America. However, Film Noir in America, which again came to the fore with WW2, borrowed from foreign filmmakers, notably German expressionism, and altered American cinema to become darker and more realistic in regards to the story and characters. The style was still heightened and this is feeding back into Europe. But the conversation is starting between American cinema and European cinema in terms of influencing each other. Ossessione is one of the films that helps bring realism back to both worlds in a way via first helping to nudge European films in the direction of naturalistic, realistic filmmaking that would then nudge American films in that direction.
This is a classic storyline that is redone in the American The Postman Always Rings Twice where you're forced to root for the murderous, cheating young wife and her lover to get away with killing her husband. It's a hard hitting story that's shot extremely naturalistically and thus helps further break down the fourth wall and make you revel in the horror of what's occurring.