While I don't think it's the best movie, ever ... my favorite movie is "I Am Sam."
No other movie moves me to tears like this one does. Sad tears and happy tears. And a lot of them.
Sean Penn absolutely deserved a Best Actor Oscar (Denzel Washington won it for Training Day, which I get) and the soundtrack (all Beatles covers by great artists) is absolutely fantastic.
I don't watch it often, but when I do, I always make sure everything around me is right. It's just a great film, all around.