Somehow it doesn't seem fair to include Star Wars in mine, since I really couldn't be sure whether I was voting for watching the film itself, or the memory of watching the film.
The Shortlist:
The Life of Brian
Magnolia
Mulholland Drive
2001: A Space Odyssey
Silence of the Lambs
Clerks
And the award goes to...
Mulholland Drive. I watched it for the first time four or five years ago, and once it was finished, I just thought, 'I don't get that at all'. Then about half an hour later, I decided I wanted to see it again, and did so. I've never done that with a film before, let alone one that is two-and-a-half hours long. Several viewings later, I think I get most of it now, but there are still some gaps. There's something special about a film that lets you do the thinking.