I hate art films. Why? Because they suffer under the delusion that there are only two options: style or substance; pick one, both cannot exist. _Belle de Jour_ shows that a movie can be both. The movie is dripping with style. Every piece of this film is captivating: the camera work, the wardrobe, the acting, the lighting, the color pallet. All of that while having an interesting story that is, honestly, like no other movie I have seen. The best I could say is that it's like an Audrey Hepburn movie, only French. What does that mean? I'm not entirely sure.
Look, I'm not going to lie, I didn't understand the ending. I mean, I think I did, but I'm not sure at all. With that being said, I still enjoyed this very much. What makes _Belle de Jour_ so interesting is what also makes it confusing: our main character, Severine, is an enigma who launches into fantasies, dreams, and maybe flashbacks, but it's not always clear what is what.
If you need movies to be very simple, you may do well to stay away. However, if you don't mind films with a few vague moments, there is much to be appreciated here.
I didn't know anything about the story before watching it, and I feel like that was the proper way to see it. Just understand that it is not "erotic," nor it is romantic - not is any traditional sense. It's a movie about sexuality, only without being overtly sexual. There are only hints of nudity, so don't expect Russ Meyer or Tinto Brass.
I don't think I'd call this a must watch, though if you're a fan of classic films - in particular, French films - you owe it to yourself to give it one view.