Well, I just recently started watching Hitchcock's films. Man, was North by Northwest awesome. So they are some (old) films that I had not seen before that were quite good. Seriously, though, how can you know the best movie you have never seen? There are plenty of movies that other people have liked that I have not seen (Citizen Kane, Lawerence of Arabia, etc.), but there is no way for me to know if they are "good" (in my terms) until I see them.