Shrek the Third (U) <img src="http://www.independent.co.uk/template/ver/gfx/twostar.gif" alt="twostar"></img>

It's monster week. You'd never see these movies on a double bill together but, oddly enough, both Shrek the Third and Hostel: Part II derive from a similar tradition, albeit drastically mutated, of Americans abroad in Europe.

After the dismal third-part instalments of Spider-Man, Pirates of the Caribbean and Ocean's Thirteen, it would not require much of Shrek the Third to raise the summer "threequel" to a level of acceptable entertainment. And as these things go it pootles along quite pleasantly, buoyed on the same mixture of tittering slapstick and arch pop-culture references that ranks it a little lower than the Pixar movies, and a lot lower than The Simpsons.

In the three years since Shrek 2, the technical wizardry has rapidly advanced to the point where one of the effects supervisors talks of the development of "new hair simulation tools allowing for more realistic motion and collisions with geometry". It sounds more like that famous cure for baldness.

While at DreamWorks they are very excited about these new technologies and the micro-fastidious detailing that they enable, one wonders if they have been maintaining an equivalent sharpness elsewhere. The pastiches taste a bit off, and the one-liners only occasionally score a hit on the funny bone. Just as Shrek 2 couldn't match the newly minted surprise of the original, so Shrek the Third can't compete for freshness with either.

Character-wise, there have been no discernible advances. Our irascible ogre-hero is still battling with the problem of low self-esteem (as who might not, with a phiz like that). In the first movie he thought himself unworthy of love; in the second he agonised about his role as consort to royalty; now, he's having the jitters about the prospect of fatherhood.

One sequence plays out an anxiety dream in which Shrek dandles his new-born son in front of him, and all seems well; then the infant – an ogreling, I suppose – burps and disgorges a torrent of green puke that blasts his father to the other side of the room. I have to admit that I laughed.

After the frog-king (voiced by John Cleese) pegs out, it devolves on Shrek either to assume the crown himself or else to seek out the only other living heir. Having no regal ambitions, he sets sail with his companions Donkey (Eddie Murphy) and Puss in Boots (Antonio Banderas) to find the rightful successor, who turns out to be a bullied student at Worcestershire High, named Artie .

This looks to be the cue for a medieval pastiche of high-school movies: I liked the drugs counsellor whose message to the kids is, "Just say nay", but maidenly cheerleaders and jock knights seem weak, as does the script: "Artie a king? More like the mayor of Loserville." They've got Justin Timberlake to voice the unfancied heir, but the character is so bland and unconvincing that they could have hired Chris O'Donnell and no one would have noticed.

With Puss and Donkey misfiring as a double-act this time around, the four screenwriters (who include the director, Chris Miller) could have compensated by introducing a really good villain. Instead, they fall back on Prince Charming, who's merely a hammy stage actor – voiced by Rupert Everett – desperate to be famous. When he goes to a tavern to round up all the fairy-tale losers (The Ugly Sisters, Captain Hook, Rumplestiltskin) the lounge singer there is maundering through "I've Been to Paradise (But I've Never Been to Me)", which is a perfect sort of anthem for these malcontents.

The subsequent plot in which Charming proceeds to stage a palace coup never really catches fire, and with Shrek delivering the usual be-true-to-yourself pep talk to Artie, one feels a bit starved of excitement. In time to come the three movies will blur into one big Shrek soup, so not much harm has been done. All the same, it would be a good idea for those involved to quit while they're still (just about) winning.