There are two relationships at the film's center—the first poignant, the second screwball-comic. Both work beautifully. Penn gets so deep inside this loving simpleton that almost every word he utters to his daughter sounds like a tender lyric, something from "Two of Us" or "Across the Universe." I don't know how such a sour guy can find it in himself to be so fearlessly rhapsodic, but that's one of the mysteries of acting—and Penn is one of the greatest actors alive. Dakota Fanning is an otherworldly gorgeous child, and she gets on Penn's wavelength and holds up her end of the love duets without missing a beat. Pfeiffer is in a different key: Her over-caffeinated rhythms (she's a Tab drinker after my own heart) make it impossible at first for Sam even to penetrate her consciousness, and her exasperated double takes in the face of his plodding literal-mindedness are some of the funniest moments in a movie all year. The rest of the actors (including Richard Schiff and a Picture-of-Dorian-Gray lovely Mary Steenburgen) hit singing notes of their own.
I Am Sam is manipulative as hell; it's too one-dimensional to be a masterpiece. It's also possible that fathers of wonderful little girls named Lucy who frequently regard themselves as "retards" need to be cut some slack here. (I am all of the above.) Just don't believe the anti-hype. There are lots of reasons to have a good cry these days—here's a nice, warm place to get squeezed.