During the classic period of film noir I believe that the content and visual elements were pretty much consistent through out that period. They all had the same story line but the events, actions, and corruption were played out different. Some film noir movies started from the end of the story first and then played out the events leading up to that point.
The films were all black and white, with dark and gloomy settings, low budget, with some sort of crime and suspense with a twist at the end. Clasisic film noir movies had corruption, gun fights, murder and an innocent person was almost always lured into a crime.Men were seduced by women and the women could almost always get a man to do whatever she wanted and that's what you would call "femme fatale". The men always got caught up with this dangerous deadly woman.
The men were dressed up in suits, fedoras and pretty much carried guns. There were always some sort of private eye or detective type character. The women in film noir movies were also always dressed well with their hair and makeup done. They were sexy, mysterious and always had a dangerous side.
I think that people enjoyed film noir during the classic period because it was during an era of peace and calm. It gave the audience a sense of excitement and suspense. I believe it's always the same type of story line but with different characteristics and a different type of corruption. I like how there's always some type of twist during the end and you don't really know what to expect.