Films about child prodigies or twentysomething geniuses rarely get inside their heads and ask: "What makes you tick?" An even tougher question rarely posed is: "How do you deal with who you are?" Slight films in this category that could have been great include Jodie Foster's "Little Man Tate," and the predictable Rocky-crossed-with-chess-playing tale "Searching For Bobby Fischer." There's also the finely acted "Stand and Deliver" that dealt with inner-city kids who miraculously performed better in A.P. Calculus exams than anyone else, but they didn't exist as anything more than ciphers. One film that broke through that barrier was the marvelous "Amadeus," which depicted the rare talents of the wonderful composer Wolfgang Amadeus Mozart in blazing glory with, naturally, great music to alleviate the senses. The Oscar-winning film was a three-dimensional portrait of Mozart presenting him as a buffoonish clown who didn't seem arrogant, but knew how good a composer he was. Now there is also "Good Will Hunting," a finely acted, well-written drama about a math genius who is too good to be true, and that is part of the film's problem.

The charismatic Matt Damon stars as the conceited orphan Will Hunting; a South Bostonian hooligan who drinks, fights, and generally fools around with his buddies. He works as a janitor at MIT and, once in a while, he solves complex math problems posed by an MIT professor (Stellan Skarsgard) on a hallway blackboard. When the professor finally spots him solving a problem, he decides to use Will as a math instructor to solve all kinds of difficult math theorems that had conflicted scientists for centuries. Will is reluctant at first, but he decides to go along with it since it is way of avoiding jail time. It also means that he has to see a brilliant therapist (Robin Williams) twice a week - a former child prodigy who will try to uncover what makes this troubled kid tick.

Will has the ability to see through people - he can make Harvard students envious with his textbook knowledge of politics, and he can drive people mad with aggravation, including the therapist who Will discovers is a widower. Lest anyone think that he's just a brainiac, Will also has the ability to love, especially a British Harvard student (Minnie Driver) who wants to help him grapple with his emotions. There's a priceless scene where he picks up Minnie at a bar. She asks if they could get together for coffee. He suggests caramels: "When you think about it, it is as arbitrary as drinking coffee."

"Good Will Hunting" has a terrific premise - a troubled genius who suppresses his past - and although the film deals with his abusive past, it never confirms or explains Will's genius. Where does it stem from and, more importantly, how does Will feel about his own intelligence? The movie treats Will as a misunderstood genius rather than allowing Will to see how he mistreats and misunderstands himself. That's probably too much to expect from a film, but I wouldn't have minded to see Will's brain at work - how about a scene where we see the mental process by which Will solves a math problem? There are some instances where we see Will's genius at work (the courtroom scenes where Will avoids misdemeanor jail sentences by quoting legal cases from the 19th century is a good example) but they are not enough to show how Will's mind unravels. Mostly, we see the selfish MIT professor trying to use Will's mind as an experiment for his own ambitions, and there's the therapist who is trying to get Will to confront his past - yes, you've seen these subplots before.

"Good Will Hunting" has plenty of expert performances from the cast, including Matt Damon ("Courage Under Fire") as the fast-talking Will; Ben Affleck ("Chasing Amy") as Will's beer-drinking buddy who has a pivotal moment where he tries to convince Will to take advantage of his talents; the luscious Minnie Driver as Will's girlfriend who loves him; and the grand Robin Williams as the hip therapist who has been down the same road as Will. Williams, in his Awakenings mode, is brilliantly understated and a joy to watch as we see him gradually trying to get Will to open his heart. His final scene, where he repeatedly acknowledges to Will that it is "not your fault," is emotionally powerful and heartbreaking.

"Good Will Hunting" is competently directed by Gus Van Sant ("Drugstore Cowboy"), but he never gets as close to Will's nature as he did to River Phoenix's in "My Own Private Idaho." The first-time screenplay by co-stars Ben Affleck and Matt Damon is often smartly funny, manipulative and quasi-sentimental but not as freshly developed as I might have hoped. By the end of the film, you feel that Will Hunting is more like an unreal movie character than a genuine, three-dimensional human being.