In theaters

K-PAX, directed by Iain Softley, written by Charles Leavitt, based on the novel by Gene Brewer, 120 minutes, PG-13.

Iaian Softley’s sci-fi drama “K-Pax” works as well as it does because of its two male leads – Kevin Spacey and Jeff Bridges – who keep the story grounded during those moments when it threatens to fly away.

The film, which Charles Leavitt based on Gene Brewer’s 1995 novel, is about a mental patient named Prot (Spacey) who may or may not be from another planet. That’s its mystery, on which everything is staked.

Audiences have seen the movie before, whether in whole or in part. The film is a mix of other movies, from “One Flew Over the Cuckoo’s Nest” to “Miracle on 34th Street,” “The Three Faces of Eve,” “The Man Who Fell to Earth” and “Starman,” which also starred Bridges.

Its true inspiration, however, is the movie it mirrors so closely: Eliseo Subiela’s 1986 film “Man Facing Southeast,” which also followed a psychiatrist’s relationship with a man who claims to be from another world.

In Softley’s film, that otherworld is K-Pax, which may sound like a potent laxative, but which is actually a planet 1,000 light years from Earth. It’s from K-Pax that Prot (rhymes with goat) allegedly hails.

But is he from another planet? After mysteriously appearing in Grand Central Station in a sudden burst of light, it would certainly seem so. But when Prot fails to convince authorities that he’s from far, far away, he’s taken to a Manhattan psychiatric hospital, where he becomes Dr. Mark Powell’s (Bridges) patient in the film’s energetic first half, undergoes hypnosis therapy in the melodramatic last half, and raises some serious doubts about whether he’s human.

“K-Pax” is of the life-affirming genre, which means a good deal of it is focused on how Prot’s snappy, mischievous charm has the power to lift and change lives. He does so for Powell, whose weary detachment has nearly cost him his relationship with his son and second wife, but he especially does so for his fellow mental patients, a colorful group of caricatures who are so absurdly cute, they’re like teddy bears on Thorazine.

The film never overcomes its insistence that the mentally ill are the equivalent of sheep in a petting zoo, an element that irritates. But it’s also true that when the story shifts to Prot and Powell, a great deal of it works, especially in those scenes where Spacey and Bridges are allowed to spar, which are so tight, they punch the material into a realm it wouldn’t have reached without them.

Grade: B-

On video and DVD

SHREK, directed by Andrew Adamson and Vicky Jenson, written by Ted Elliott, Terry Rossio, Joe Stillman and Roger S.H. Schulman, 90 minutes, PG.

After gobbling up $270 million at the summer box office and becoming the 13th highest grossing film of all time, Dreamworks’ “Shrek” stomps into video stores with 11 hours of additional material – not to mention a new ending – on a two-disc DVD set.

The film follows Shrek (voice of Mike Myers), a giant green ogre with a Scottish brogue who’s forced to leave his peaceful swamp when it becomes overrun by a bickering band of fairy-tale has-beens.

Not just any fairy-tale has-beens, mind you, but Disney’s Snow White and the Seven Dwarfs, Sleeping Beauty, Cinderella, Tinker Bell and Pinocchio.

As overseen by DreamWorks’ animation chief, Jeffrey Katzenberg – a man who once had a famous falling out with his former Disney boss, Michael Eisner – “Shrek” is essentially 90 minutes of gleeful Disney-bashing, a wicked little film that couches its mean streak in the softer edges of an ongoing, pop-culture joke.

What’s so smart about the movie is that its pleasures go beyond Katzenberg’s schoolyard bullying. The film features Shrek reluctantly hitting the road with a talking donkey named Donkey (Eddie Murphy) so he can deliver the beautiful Princess Fiona (Cameron Diaz) to Lord Farquaad (John Lithgow), a grim little man who wants to marry Fiona so he can become king.

Shrek’s motivation? Only after Farquaad weds Fiona will he return Shrek’s swamp to its once pristine state. The story’s complication? Shrek, rather predictably, falls for the princess, who has a secret she doesn’t dare to share.

In spite of dawdling at its midpoint, “Shrek” nevertheless peppers the action with enough ribald moments and wit to please children and adults. It’s at its best with its superb computer animation and when it snubs its nose at pop culture, elements that made it the animated movie of the summer – and, if tonight’s “Monsters, Inc.” doesn’t score with audiences, perhaps the animated movie of the year.

Grade: A-

Christopher Smith is the Bangor Daily News film critic. His reviews appear Mondays and Fridays in Style, Tuesdays on “NEWS CENTER at 5” and Thursdays on “NEWS CENTER at 5:30” on WLBZ-2 and WCSH-6. He can be reached at BDNFilm1@aol.com.