It has a good humanitarian side to it; it is a reminder that mentally challenged people deserve to be treated kindly, and that sometimes they are more capable of giving love than people with better I.Q.s.
Sam adores his daughter, who loves him just as much but she is smart enough to notice that her mental capacities are superior to his. They share such a wonderful complicity that I find it hard to believe that a father-daughter relationship can be that solid. The premise is incredible. No one ever raises any questions about Sam's ability to raise his daughter until she is seven! Sam is the father every child wishes to have: he is caring, patient, loving, giving and selfless. He cares too much for her and not enough for himself; I'm no psychiatrist but it is commonly believed that autistic people are much more self-centered than that!
Another unrealistic part: with all due respect to mentally challenged persons, I doubt that a restaurant as popular as Pizza Hutt and a coffee shop as famous as Starbucks would actually hire someone like Sam, regardless of his position.
Moreover, everyone in this movie seems to be afflicted with some sort of a mental or emotional problem. Lucy suffers from anxiety, Sam and his close friends are all mentally handicapped, Rita has problem communicating with her son and her marriage is falling apart, Annie has not left her room in years, and even one particular doctor who testifies against Sam in court has developed a guilt pattern because her son died of an overdose.
All of these elements combined make the viewers feel they are being manipulated in a somewhat obvious manner.
Finally, let's be objective here: the whole movie focuses on reuniting Sam and Lucy, regardless of Sam's handicap and how the latter would lessen the girl's mental and educational growth. Undoubtedly, Lucy would never find a more loving father, but she also needs 'regular' people's guidance and besides, he needs assistance himself!
The filmmakers were obviously not sure how to end the movie in a believable manner, therefore the ending was ambiguous. Lucy most probably ends up being "shared" by Sam and her foster family, Rita seems to have regained her son's trust, and Sam's mentally challenged friends will have the same habits for the rest of their lives, like video night every Friday.
So I guess that is a (sappy) happy ending. Again, not very believable and too many questions are left unanswered.
Overall, the movie is good; it is very moving and at times, it does put a smile on your cynical face. :) Everyone gives an excellent performance, even Fanning, though I find her character a bit too smart and perceptive for her age.
The soudtrack rules! But then again, I'm a Beatles addict, so it's hard for me to be objective. I enjoyed the scenes of Sam and Lucy together and how certain Beatles cover songs fitted the mood and situation. Sam is a Beatles freak himself; he named his daughter Lucy Diamond after "Lucy in the Sky with Diamonds" and throughout the movie, he uses analogies related to the band's life and songs to express his feelings and point of view; those portions of the script are clever and make his character interesting and rather 'creative' compared to, say, Rainman.
Fortunately, the movie did not stay in the courtroom and ended on a football playground.
"I am Sam" has garnered Sean Penn a Best Actor Oscar nomination, and he truly deserves to win that award.