Saw this recently. It's still a fine film indeed, and the haunting sequences are still masterful. Many films are about the supernatural, but to be honest very few give you the eerie sense of something supernatural at work. This is certainly one of them.
Another word about Armchair Thriller. Yes, the faceless nun made the blood run cold, but I was also creeped out by the title sequence, where a ghost/shadow walks across a room and settles into an armchair. I know it was only a bit of animation, but still.