Finally. An airtight excuse for truancy. "There's no school today because of the aliens," 10-year-old Jacob (Jaden Smith) deadpans to his concerned stepmom, Helen (Jennifer Connelly), a Princeton astrobiologist whose expertise is needed but pronto.

Emerging from the colossal fireball that has descended upon Central Park's Great Lawn are Gort, a one-eyed steel giant, and Klaatu, an adult humanoid encased in what appears to be whale blubber.

First, the Earth trembles. Then, it holds its breath as Klaatu (Keanu Reeves, resembling a cross between young Al Gore and middle-aged Dorian Gray) demands to be taken to our leader. He doesn't mean POTUS.

The Day the Earth Stood Still, an entertaining rethink of the 1951 classic warning against nuclear war, follows the general lines of a lightbulb joke. How many astrobiologists does it take to change the Earth? One - but the Earth has to really want to change. And in this film (largely set in New Jersey, but shot in British Columbia) it's change or die.

Connelly, a doe whose inquisitive celadon eyes have unexplored depths, is one of the loveliest things in movies. Her expression of skepticism giving way to awe sets the tone for the film. In the first two-thirds of the film, director Scott Derrickson (The Exorcism of Emily Rose) understands that the human face - especially that of Connelly - is more expressive than any special effect. In a movie that needs proof of why saving humanity is as important as saving the Earth, Connelly is its best argument.

Moviegoers are evenly divided into two camps, those who believe that Reeves is a cinematic black hole and those who believe that his Zen equilibrium suggests a heroic balance of opposing forces. I'm in the latter camp. His placeless quality makes him the right man for Neo in Matrix and Klaatu here.

A correspondent observes, "If what you want is an actor to suggest that human speech and movement are alien to him, Keanu's your go-to guy." His early scenes as Klaatu, where the alien life-form has to acclimate itself to a human body, suggest that of a toddler taking its first steps - or Jeff Bridges in Starman. The actor is particularly well-matched with Connelly, who appears to challenge him to an intense-off. It's a draw.

If Connelly is of the less-is-more school and Reeves the less-than-zero-is-more type, Jon Hamm - Don Draper on Mad Men - is some sort of generic scientist who doesn't get into the minimalist groove of his costars. Nor does the adorable Jaden Smith (son of Will and Jada Pinkett Smith), who has inherited the genetic gift of commanding the screen.

For its first hour, the film smartly relies on the human factor and the power of actors' faces in extreme close-up. But in an attempt to up the ante in this high-stakes game of Earth vs. earthlings, Derrickson shoots the moon with swarms and explosions. While it doesn't undermine his affecting setup, neither does it advance it.