Some movies are complex stews: They taste richer the second time around when all the flavors reveal themselves. I find this most true with comedy and mystery. In funny movies I'm laughing so hard I don't catch all the jokes the first time around. In mysteries, on repeat viewing I see how and where the filmmakers have seeded the story. It wasn't until the third time I saw The Godfather that I could tell Tessio from Clemenza.
Recently Amy B asked for movies that fit the "Once is Not Enough" rule: Here is a provisional list, to which I'd add most screwball comedies and movies with fractured narratives and surprise endings. Just as certain music grows on you, so do these films.