I would call this movie a "near masterpiece" that falls short. In many respects it's not your typical gangster flick. It contains violence that is more graphic than most mainstream gangster films, yet also delves into the characters personal lives at a much deeper level than any other gangster/mafia films I have seen. This movie was originally intended to be two movies but was edited down to very long single film for European release. The original US film release was edited down much more to the point that it was basically unwatchable. There was also a TV version that was longer and the scenes were re-arranged into chronological order. That was better than the US theater release, but they did cut out all the graphic violence and other pertinent scenes.
The current version playing on Netflix is the best of the 3 versions I have seen. It is my understanding this is the original Europe version, or close to it. It runs 3:45, so I watched it over 2 nights. Part of the reason I think people don't like this film is none of the main characters have many redeeming qualities. They are not likable people. I think US audiences tend to have a problem with that. The movie is long, but not boring in my opinion. It draws you in if you let it. I have a feeling that most of the folks that say this is boring say the same about 2001, which is a masterpiece.
My main critique of the movie is that the scenes when the characters were children in 1920 seem very drawn out, while some of the scenes set in 1968 seem truncated. The 1968 scenes were heavily edited down I believe when the movie was combined into a single release. Youtube has some of the edited 1968 scenes if you want to see them.
The movie contains a lot of symbolism and leaves some questions for the audience to decide/interpret. I like that.
I can see how Tarantino was influenced by this movie, and probably Coen brothers as well. Not for everyone, but serious film geeks should definitely check out the Netflix version. Cheers