"I Am Sam" really gets to you in a meaningful way, and it’s hard to believe it isn't destined to be considered a classic—it almost makes me wonder about people’s judgment. Sean Penn delivers what feels like the defining performance of his career; he’s far more impactful than Dustin Hoffman was in "Rain Man." That portrayal is already nearly perfect on its own. Dakota Fanning, who plays Lucy, also stands out remarkabl…