There are two tests in my mind for a classic film.
First, it must plant some images permanently in your life. Very few films do that. Two films that are cogent to discussing this one are Helena Bonham Carter's Ophelia in Zefferelli's `Hamlet.' She and Glenn Close acted circles around the guys -- her expression in the midst of the play within the play is lasting over years in my memory. The whole film revolves around that moment.
Also lasting are several images from the ostensibly unambitious `Oscar and Lucinda.' But I also carry many lasting film images that are junk, courtesy of Lucas and Spielberg. That brings us to the second condition: for a film to be classic, evocation of the images, the remembrance, needs to be multidimensional, to elevate rather than dumb down.
Measured by those rules, this film is remarkable. For a few years, I have carried the image of the next to last scene where Carter makes love and in the act discovers the truth about her love. This is so wonderful, so tragic, so true that it has stuck with me, together with the secondary images, the memories of Venice and Millie that Merton is in love with. I hope to follow this woman's career for decades. I wonder where it will go?