We've had plenty of proof this summer that third instalments of popular blockbusters are either exceptionally difficult to make or rather less fresh than your average wilting daisy. Not one of them has been a good surprise. Shrek the Third is the worst case in point. I have rarely seen a more feeble piece of story-telling in aid of animation that, at its best, is state of the art.

The recipe hasn't changed much, even if the cooking is underdone. John Cleese's dying King Harold names Shrek (Mike Myers) as heir to the kingdom of Far Far Away. The green monster is fretting about impending fatherhood and doesn't want the extra burden, so sets off with Donkey (Eddie Murphy) and Puss in Boots (Antonio Banderas) to find a suitable replacement.

Gallery: See more stills from the film here

While they are away, nasty Prince Charming (Rupert Everett) seizes control and imprisons Shrek's pregnant wife Princess Fiona (Cameron Diaz) along with Queen Lillian (Julie Andrews) and Snow White (Amy Poehler).

It's up to Shrek to defeat the villains and, being a decent sort, he does so by appealing to their better natures. There's a ghastly syrupy ending to emphasise that good will always beat bad and all's well with the world.

There are, of course, a few genuinely funny moments and a sprinkling of decent one-liners. There's also nice homage to Rosemary's Baby and you have to laugh when Andrews suddenly sings a line from My Favourite Things. You will enjoy the moments when Shrek tries hard to be an effective King before giving up on the job.

But the rest is poorly written and dully characterised. Even the cast seem less enthusiastically bouncy than before. The product placement is pretty blatant, too. It looks very much as if there was no creative reason whatsoever to make the movie apart from the fact that its predecessors made a heap of money.

This may be a good way to get rich on the franchise, and there's no doubt that Dreamworks will. But there can't be another episode in the pipeline unless it is decided to erase the memory of this one which simply doesn't achieve what the first two films managed: to appeal to kids and parents as well.