By common consent, though not, so far, that of the Motion Picture Academy, Sean Penn is the great actor of his generation. In a twenty-year career (he is 41) he has stunned us with a range of work far beyond that of any of his contemporaries: "The Falcon and the Snowman," "Casualties of War," "Dead Man Walking," and "Sweet and Lowdown" come to mind, among others. And now, in "I Am Sam," he plays a retarded man with a mental age of seven, who has fathered a bright daughter who is now also seven. The film deals with the question of whether he should be allowed to keep custody of her. For Penn this is not an acting exercise. He comes as close to being Sam Dawson as anyone of normal intelligence can come, and he makes no use of the kinds of technical tricks and tics that lesser actors rely on. We in the audience can see that Penn sees the world through Sam's eyes.

But as fine as his performance is, he is confronted with a script and direction that are focused so tightly on event and episode - will he lose custody of his child, how will he handle the court hearings, does he understand what it means to parent a child, will he help his attorney (Michelle Pfeiffer) win the case, and even can he make coffee at the Starbucks where he works - that the Sam we see is almost submerged in all the film's plot points. And in the attempt to hurry us along from one to the next, the film does a disservice to its very goal; it refuses to let us make up our own minds.

Pfeiffer, who has done some very good work in the past ("Married to the Mob," "The Fabulous Baker Boys") here plays a role that comes right out of the Screenwriter's Guide to Clichéd Characters: the harried, rich, selfish and self-centered, high-powered attorney with a failing marriage and a neglected son (by an uncanny coincidence also seven years old). She takes on Sam's case more by accident than desire, and, you'll be happy to hear, learns an important life lesson from it. I'll leave you to guess what it is.

Sam's daughter is played by Dakota Fanning, and she is the most winsome, lovely child in ages; she completes the relationship with Sam by being a true daughter: babyish, adult, selfish, thoughtful, and always wonderfully alive and warm. There is an extraordinary scene in which he is reading "Green Eggs and Ham" to her in bed, which he does every night. And when he tries to read another book, which he cannot, she asks him to read "Sam" again. She knows it is the only book he can read.