I've seen all of them. The one thing that all of the films have in common is the plot progression. All of them are character studies. I didn't have the patience for 2001, or Blade Runner. They are both beautifully shot films, but they weren't for me. All of them are worth watching.
It's a matter of taste, but I can't understand being bored by The Godfather. Bogart, like John Wayne, are their characters in all their movies. I can only understand disliking Casablanca, if you don't like Bogart. Taxi Driver is a bleak movie. It was still very powerful, and well done. Meh, you get the idea.
If you want to see a positive character driven movie, The Apostle, with Robert Duvall is great. It's still a little tough. It's worth it.