There are several 'classic' movies I've tried and just couldn't force myself to sit through. I can't think of any I haven't actually seen.
The thing with a lot of classics, at least IMO, is that they represent a certain time. Casablanca I heard was phenomenal. Well my hubby and I watched, and I did realize how many sayings come from that movie, but I thought "this is what the big fuss is over". But, that's how it goes. My mom told me to watch One Flew Over the Cuckoo's Nest, and I did love that one, and that one isn't as old as Casablanca obviously.
I thought I'd love Vertigo since I love Hitchcock, but again, it was very underwhelming for me.
Let me specify: I loved Hitchcock Presents when I was young. It came on Nick at Nite. I haven't seen many of his films.