Flubber, the substance, has more personality than many Hollywood actors. And if Flubber, the movie, isn't quite a slam dunk, at least it's a relatively bouncy way to spend an hour and a half.

Despite a couple of slow stretches along the way, director Mayfield does a generally fine job of integrating the eye-popping special effects with the simple but serviceable plot. The pace is just brisk enough to satisfy youngsters with short attention spans, and Williams is winning enough to keep audiences of all ages involved.

In fact, there are times when this movie feels like the latest installment in the over-milked Home Alone saga.

Though Mr. Williams sometimes seems on the verge of "Aladdin"-caliber improvisation with the ever-morphing green flubber, the film bogs him down with a fiancee (Marcia Gay Harden) hellbent on making him remember a wedding date, and with the full Hughes retinue of thugs and bullies.

With the exception of the handful of scenes in which the Flubber does its stuff, however, the youngsters will no doubt be bored by it all.

The more pathetic the role, the more evident Robin Williams's conscientiousness--but his professionalism doesn't make this fantasy worthwhile.

Remember when John Hughes made small, original, oh say, GOOD movies?

Let's blame it on poor Robin Williams, who tries so desperately to be likable, whimsical, lovable, smart and funny all at once that he just wears you out. Blame it also on the behind-the-scenes engineers at Disney who think that effects are more important than story and character.

Although the movie may appeal to kids in the lower grades, it's pretty slow, flat and dumb.

It's a perfect fit for Williams -- a hunk of slapstick, a dose of schmaltz -- and yet he can't save the film, which is overproduced, mechanical and resoundingly unfunny.