For whatever reason I was thinking of One Flew Over the Cuckoo's Nest today. Why did it have such an impact? The movie feels very real. Cinéma vérité style realism isn't the only way to go, of course, but it the context of Hollywood at the time it was new and fresh. The camera finds the action, the source of conflict in the scene, of course. But its view is unsettled, as if it were another person in the room not quite sure where to look.
Casting enhanced this feeling. Jack Nicholson was the only actor anywhere near being a star. Louise Fletcher had done a lot of TV guest roles, but very few films up to that point. A few supporting roles were filled by non-actors.
Seen above, Christopher Lloyd was experienced onstage, not much known outside of it. It's different now, and strange seeing him as a borderline abusive mental patient. Also, it's weird to see him with such short hair, especially in the seventies.