Alternately sensitive and cloying, Martian Child sometimes feels as if it were written and directed by extraterrestrials trying hard to copy the "tearjerker" formula created by earthlings. There is much to admire in this well-intentioned saga about a single man who adopts a troubled little boy, particularly the interaction between stars John Cusack and young Bobby Coleman. But too many moments of low-key emotion are tempered by clumsy melodrama that hits the right superficial notes without managing to capture genuine heart.

When the movies need an actor of shaggy earnestness and quiet decency, Cusack is the go-to guy. And for good reason. In Martian Child, he gives a direct, moving performance as science-fiction writer David Gordon. Despite his professional successes, David is hurting, still grieving the death of his wife two years ago. He resolves to adopt a child, a plan that he and his wife had shared but weren't able to fulfill in her lifetime.

But David doesn't adopt just any kid. He is drawn to Dennis, a pale, quiet 7 year old who spends most of his time wearing a weight-belt while safely hidden under a big shipping box.

Dennis, you see, says he is from Mars. The boy says he must protect himself from the sun and Earth's weak gravitational pull.

David's sister Liz (Joan Cusack, the star's real-life sister) warns her brother that a kid in a box is a giant red flag, but David is unmoved. In this strange boy, David sees a reflection of his own awkward and painful childhood. He wants to help Dennis, to let the child feel loved and subsequently dispense with the Martian fantasy he wields to keep the world -- and its potential disappointments -- at bay. While David agonizes over whether he is ready for the challenges ahead, he does not waver in his determination to try.

Martian Child is at its most affecting when David and Dennis are tentatively learning about how to deal with the other. Coleman is surprisingly restrained for a child actor; he and Cusack settle into a guarded tension that lends resonance to their interaction. There is also a fine lineup of supporting players, including Oliver Platt as David's agent and Amanda Peet as the best friend of David's late wife.

If only the movie was as consistent as its cast. In an effort to pump up conflict, screenwriters Seth E. Bass and Jonathan Tolins resort to some wheezy plot devices. A stern child welfare worker (Richard Schiff) seems all too eager to yank Dennis out of David's home, an odd stance considering the orphan isn't likely to find another foster parent anytime soon. And the movie telegraphs a climax so desperate to tug at the heartstrings, it borders on embarrassing.

Director Menno Meyjes (Max) too often lets the film vacillate between poignancy and mawkishness. In one nighttime scene, the Martian child wanders around an extravagant Christmas display in a front yard. It's a lovely moment, but it does not last. Shortly thereafter, the audience is enduring the manufactured frivolity of giddy David and Dennis smashing plates in a kitchen and squirting each other with ketchup. And, of course, the stern ol' child welfare worker picks that precise moment to pay an unscheduled visit.

Such missteps are jarring, but not altogether fatal. Martian Child, based on a novel by sci-fi writer David Gerrold (perhaps best known for penning the Star Trek "Trouble with Tribbles" episode), is unabashedly sentimental. Anchored by Cusack's likeable performance, the movie celebrates the critical business of raising a child, and the paradox of wanting your children to be themselves without attracting the cruelty of others. Surely, there is room in this cynical world for such a film, however imperfect it might be.

The picture, in anamorphic widescreen (1.85:1), is excellent quality -- sharp lines, nicely detailed and vivid colors. The review DVD had a brief second of pixilation about an hour into the film, but that could well have been unique to the screener.

The Dolby Digital 5.1 Surround is clean and crisp, with no noticeable distortion or drop-out. Audio is also available in 2.0 Stereo Surround. Optional subtitles are in English and Spanish.

A commentary features producers Corey Sienega and David Kirschner, as well as screenwriters Seth Bass and Jonathan Tolins. The vibe is laidback, friendly and informative. Notably absent are Cusack and director Meyjes.

Handle with Care: Working with the Martian Child (24:20) is a comprehensive, if too-polished, featurette about 8-year-old Bobby Coleman and how he worked with Cusack, the director and others. The Real Martian Child (13:23) focuses on sci-fi writer David Gerrold and his real-life experiences with his adopted son. Fourteen deleted and additional scenes have a total running time of 27 minutes and 15 seconds, and are of mild interest.

Included are a theatrical trailer and sneak peeks for Run, Fat Boy, Run; The Last Minzy, Gracie, Hairspray and August Rush.

Viewers with an aversion to sentimentality should keep walking. For those with a soft touch, however, Martian Child is worth at least a rental. While uneven and occasionally too sappy for its own good, this family-friendly flick still garners enough lovingly rendered moments to squeeze out a few tears.