Once the movie heads off to Artie's school, it's all downhill.  The way the kids talk in a combination of proper English and Valley slang is amusing (the "Just Say Nay" campaign didn't reach the kids smelling incense in a carriage), but the humor drops off steadily from here on out.  Soon, the quartet is shipwrecked on an island where they meet Merlin (voice of Eric Idle), Artie's old magic teacher who had a nervous breakdown and now has new age tendencies.  There's a long spot here where the laughs are all but missing, and even Shrek and Artie's heart-to-heart about their callous fathers doesn't give us a connection to Artie or a further level of one to Shrek.

Shrek's really dealing with his fears of becoming a father himself, and there's a very funny dream sequence that starts off with him trying to handle a swarm of baby ogres and ends with him naked on graduation day (a Freudian slip within a Freudian dream?).  Fiona's storyline back at home isn't much better off.  She's left to fend against Charming with the help of her ladies-in-waiting, who include Snow White, Sleeping Beauty, Rapunzel, and Cinderella (whose vocal work is done by "SNL" alums Amy Poehler, Cheri Oteri, and Maya Rudolph and Amy Sedaris, all of whom are left with little to do).  In the previous movies, these characters would have been the butt of a few jokes, but here, they're inventing feminism—burning a bra and kicking ass.  It's amusing, but still, there's nothing here.  Cinderella has a Gollum complex, Snow White likes Led Zeppelin, Sleeping Beauty has narcolepsy, and Rapunzel's got a dark side.  With the addition of these new characters, all the characters—new and old—end up on the sidelines.  Nothing is developed with those we've come to adore from the previous films, and nothing makes the new ones seem like worthy additions.

There are a lot of small moments and gags that work (Charming's falsetto, the Gingerbread Man's life flashing before his eyes, and a well-placed horn to block out Puss' description of soon-to-be father Shrek come to mind), and they make for a somewhat entertaining experience.  Shrek the Third just doesn't live up to its predecessors.  Even our old friends are left in the dust, and in one of those "that's the best they could come up with?" moments, Donkey and Puss switch places.  Not before Donkey asks Puss how babies are made.  That's an odd question coming from a donkey that has apparently mated with a dragon.