I have not read the book and I still have no interest in watching a movie about a bunch of pre-40s gangsters. (I also have no interest in reading the book.) Honestly, it blows my mind that so many people are interested in that. I find it mind-numbingly tedious and unpleasant to watch. Violence, fear, tyranny, sexism... I don't like any of that stuff. Anytime I've been forced to watch any kind of "gangster" film, I've always found myself rolling my eyes and asking how long until it's over, even as other people are at the edge of their seats.
It may also have something to do with the fact that I can't relate to "family" being in any way significant in life. My family is something I simply don't think about anymore after a horrible abusive childhood, and as soon as I was old enough, I just got up and left, moved halfway across the world. I can never understand in these gangster films why the "family" feels obligated to stay together when they could just get on a plane and leave the country. Or why you would choose to protect a family member who treats you badly rather than help someone unrelated who's good to you. It's all just nonsense to me.
And anyway, the story and images and themes of the Godfather are so ubiquitous in media nowadays that I already pretty much know the story and all the most famous lines even without watching the film.
On the other hand, I second Dead Man. Surreal, psychedelic stuff, extremely well done. Funny, emotional, mind-blowing at times. There are so many moments in that film where I just feel like YES! Why don't more films do THIS? And the characters are just amazing. Plus, the music is awesome.