I have occasional movies that I really like and can't really say why. John Gruber has a Mac-related blog, but he really dotes on Stanley Kubrick, and Gruber has this quote by Kubrick: The test of a work of art is, in the end, our affection for it, not our ability to explain why it is good.
I think that works for me for "Princess Bride," for example, where that affection exists not only between me and the movie, but between the movie and me; I felt the affection between the characters, between the director and his cast, and it flowed over to me. That affection exists between the characters in "Casablanca," too, where all Rick's employees know he's really a good guy, and they like him -- they really like him.
I'll keep this new metric in mind and see how it works with movies I see.