"21 Grams" -- directed and co-written by Alejandro Gonzalez Inarruti ("Amores Perros") -- is the kind of film that has Oscar written all over it. It's got strong performances by Naomi Watts and Benicio Del Toro and it's pure Hollywood but with an artsy feel and a melodramatic performance by Sean Penn. What more could a film want?

Well, "21 Grams" could want a bit more clarity, perhaps, and maybe a bit less bluster and a little more subtlety from Penn. That said, the film, about a heart transplant recipient and his quest to find the family of the heart donor, is one of the better films to hit mainstream screens this year.

Cristina Peck (Watts) loses her husband and two daughters in a terrible freak accident and her life is destroyed. Unable to function, she stops seeing friends and communicates little for the first few months after the tragedy. But when she goes out to a club and sees a friend, she begins to take drugs again and she meets Paul Rivers (Penn), who drives her home when she's unable to do it herself.

Soon, she runs into him at a restaurant and outside the pool where she goes for her daily swim. They begin to talk and soon they become lovers; this, despite the fact that Paul Rivers is married to Mary (Charlotte Gainsbourg), who helped him recover from his heart surgery and is trying by any means to have their baby.

But the Rivers' romance is on the rocks and Paul needs Cristina as much as she needs to rekindle her life. Part of her healing involves confronting her desire to exact revenge on the man who killed her husband and daughters.

That man is Jack Jordan (Del Toro), a ne'er-do-well petty criminal who has been in and out of the can. Having found Jesus, he is involved in a storefront church, but even his desperate attempts to be pious don't seem to work too well. When he counsels young toughs, he ends up in fistfights with them. His constant preaching and his unusual take on Christian teaching - especially as he translates it into child-rearing - is causing him trouble with his wife Mariannne (Melissa Leo).

The film has a complex layered narrative that adds some depth to the story, but also occasionally renders the storyline a bit confusing as it jumps forward and back in time.

Watts and Del Toro dish up passionate and measured performances but Penn is his usual mix of petulant, angry and fiery, which works sometimes and seems rote at others. Some of the actors portraying second-string characters do the best work, especially Leo as Marianne Jordan, who isn't afraid to speak her mind to her man but is equally quick to defend him and her childrens' future when trouble arrives.

"21 Grams" -- which gets its name from a purported fact, related in the film, that everyone immediately loses 21 grams of body weight at the moment of their death; could this be the weight of the soul? -- is a visuallly satisfying film albeit with a few narrative and performance hiccups that prevent it being a masterwork.

"21 Grams" opens Fri., Dec. 26 at Landmark's Oriental Theatre.