The summer of 2007 may provide the perfect laboratory for studying the curse of the third installment. Film producers seem determined to milk the cash cow of their blockbuster franchises that fateful third time in spite of the fact that history argues so emphatically against it.

In the past, to be sure, we've had anecdotal failures served up as cautionary tales - the bathos-fueled implosion of "The Godfather 3" or the dreary third (sixth, ninth, or whatever) installment of "Star Wars" drivel-ization of a pretty promising idea.

But never before have we had such a rich mine of sequels to ponder; 2007 has seen a rush of third installments head toward the sea cliffs like lemmings in bathing caps. Bourne, Spidey, The Ocean Boys, and Captain Jack Sparrow have all strut their stuff one more time and to varying degrees of tepid applause.

But none of them has proved the virtue of quitting while you're ahead quite as powerfully as "Shrek the Third"

The plot of "Shrek the Third" is nothing to write home about. From his deathbed the king of Far Far Away informs Shrek (Mike Myers) that he's in line to inherit the throne along with Fiona (Cameron Diaz). Shrek is a reluctant ruler and realizes the only way to dodge this gilded cage is to persuade Fiona's cousin Artie (Justin Timberlake) to take the throne instead. Shrek, Donkey (Eddie Murphy), and Puss in Boots (Antonio Banderas) set off to fetch young Artie from Worcestershire High School. While Shrek is away, Prince Charming (Rupert Everett) sees his chance to stage a coup. Of course, all sorts of hilarity and pandemonium ensue.

Fortunately, the genius of "Shrek" franchise was never in a compelling story line, but rather in a delightful sensibility. Not quite the "Care Bears" and not quite "South Park", "Shrek" combined sugar and spice like few family films. On one hand we witness Fiona bravely affirming her inner beauty on the other we find out that Pinocchio wears women's underwear.

Moreover, "Shrek" had a Midas touch for character development. Donkey is one of those rare family film characters on a par with Captain Jack Sparrow plus lightning struck twice in "Shrek 2" with the introduction of Puss in Boots. With that kind of creative equity how hard could a third "Shrek" be? Too hard, it seems, for a creative team that has run out of steam.

The sly satire of popular culture has become heavy handed and obvious. Artie's trials at Worcestershire High are a rapid-fire succession of clich