Filmmaker Chris Columbus wouldn't know subtlety if it hit him on the head with a cold robotic fist.

Needless to say, that's what he uses to drive home his points in "Bicentennial Man," a sappy mishmash of two well-regarded science-fiction works — the late Isaac Asimov's short story of the same name and Robert Silverberg's novel "The Positronic Man."

But this subject — about an artificial lifeform trying to become human — has been done much better in "The Wizard of Oz" and "Pinocchio," as well as several episodes of "Star Trek: The Next Generation" about Data, the android.

And even though it is rated PG, "Bicentennial Man" features some surprising discussions about sex — and a pair of scenes regarding sexual relations and right-to-die issues — that seem out of place here, and which send some fairly troubling messages.

However, despite its heavy-handedness and nonstop sentimentality, "Bicentennial Man" isn't unwatchable. And most of the credit for that goes to Robin Williams, who is fascinating even when the material isn't.

Williams stars as the title character, an android servant for the Martin family. Though technically his name is NDR-114, he is nicknamed Andrew by the youngest daughter, Amanda (Hallie Kate Eisenberg), who becomes his closest friend.

And as the members of the family grow older and more comfortable with Andrew, they begin to notice that he exhibits such human characteristics as creativity and emotional attachment.

So Andrew receives the first of a series of physical "upgrades," designed to make him more aesthetically pleasing — if not closer to his ultimate goal.

Unfortunately, he's still not "there," and as an immortal being, he also witnesses the deaths of the family, including patriarch Richard (Sam Neill) and his beloved Amanda (Embeth Davidtz).

With help from a radical roboticist (Oliver Platt), Andrew decides to take another big step by having artificial organs and a nervous system installed in his body — which will allow him to feel sensations, and to love Amanda's granddaughter, Portia (Davidtz again).

The story is supposed to take place over two centuries, but at 132 minutes, the film feels at least that long.

It doesn't help that Columbus and screenwriter Nicholas Kazan treat some heady subject matter (such as the nature of man and object of life) in a superficial manner. Their intent is not to provoke thought but to wring out laughs with bad puns, and drama with bad melodrama.

Fortunately, the special effects are pretty dazzling (though some of the designs are a tad unoriginal), and Williams really does give it his all. As Andrew, he effectively gives his character a range of such recognizable human traits — from comical naivete to childlike curiosity to compassion and even jealousy — that without him, the film would have been much worse off.

Williams' co-stars are much less consistent. Both Neill and Davidtz seem oddly aloof, though the always-steady Platt does manage to steal the handful of scenes he's in.

"Bicentennial Man" is rated PG, though it does feature scattered profanities (done for comic effect), as well as some sexual talk and other vulgar humor (including a flatulence gag).