NOW here's a thing. I like a good weepie as much as the next mum...

But it has to be good.

And, for the most part, Pay It Forward is excellent. An interesting premise, superb performances from the three lead actors and a slightly offbeat feel accentuated by the movie's score and the intrinsic otherworldliness of its Las Vegas setting.

Then there is the final reel. All the good work of the preceding 100-odd minutes is torn to shreds by the last lachrymose half-hour in which the schmaltz is trowelled on and cemented by barrel-loads of sugar.

When new teacher Eugene Simonet (Kevin Spacey) sets his pupils an assignment designed to inspire them, he doesn't expect any of them to succeed. Their task is to come up with a scheme that will change the world.

It's a tall order but young Trevor McKinney (Haley Joel Osment) rises to the challenge. He decides that if he performs three acts of random kindness, and the beneficiaries of those favours pay them forward (instead of back) by doing three kindnesses for three strangers, the world would be a much better place. Even allowing for failures and those who simply wouldn't bother, the honour system would still work.

Trevor's motivation is largely born of his hopeless alcoholic mother Arlene (Helen Hunt). She has a good heart but a weak spirit, succumbing to the bottle at the merest hint of stress despite holding down two jobs to make ends meet.

Spacey is effortlessly excellent as the disfigured teacher, slightly shuffling, dull-eyed but sharply intellectual; while Haley Joel Osment manages to be both child-like and old-before-his time, proving his turn in The Sixth Sense was no lucky strike. And Helen Hunt adds depth and personality to the usual Hollywood drunk, drawing Arlene as aspirational trailer trash, fully aware of her shortcomings, by turns brashly ugly and defiantly beautiful.

Had the film drawn to a close at the point where Trevor revels in watching wrestling on TV it would have been knocking on the door of a perfect ten. However, we have to endure Jon Bon Jovi as Trevor's dad, Jay Mohr as an irritating reporter on the trail of the Pay It Forward Cult and Angie Dickinson as a bag lady with too big a part in the story ... and that's before we suffer the grotesque emotional manipulation of the close.

On balance, it's worth seeing, but be warned you'll feel cheated out of a better ending.