For those of you that rather enjoyed Shrek and Shrek 2, and then felt thoroughly let down by the utter dud that Shrek the Third was, you'll be pleased to know that the final instalment is NOT like Shrek 3.
Overall moral of the film: Be grateful for what you've got.
Plain and simple, and easy to fill out an enjoyable storyline as Shrek realises this moral when he's been duped by the legendary Rumpelstiltskin. You'd think Shrek'd have heard of this tricky little pixy, but no, apparently he was the only person that didn't quite click when he heard the name, so desperate was he to experience just one day that wasn't the mundane married life in which he was beloved by all - even the villagers that once chased him with pitch forks. The audience knows, whilst Shrek doesn't, that lil' Rumpel has a score to settle with him for indirectly costing him his own dream.
Whilst Shrek learns this valuable lesson of life (and that ogres can blow through their ears like bugles), he sees what life would be like without him - Fiona is an embittered warrior fighting for the freedom of ogres, Puss is a retired pampered fatcat, and donkey is a donkey. He still talks, but he does what donkeys do: pulls carts, gets hit with a whip and generally abused.
Rumpelstiltskin, through his deal, has acquired what he wanted all along, from before Shrek rescued Fiona out of the blue: the kingdom of Far Far Away for himself, which is run by him and his enormous hoard of witches.
The ending is rather touching, as Shrek tells the alternate-universe Fiona that he enjoyed falling in love with her all over again, before everyone else realises that he'd succeeded (of course!) in breaking the contract signed with Rumpelstiltskin, spiriting them all away back to just before Shrek had stormed off to see Rumpel in the first place.
The film is funny, fairly fast-moving and colourful. It isn't perhaps quite the greatness of the first two, but I'd still consider it the rightful Shrek 3 (yes, I have disowned that poor version from 2007) and buy it on DVD. Maybe.
The credits end with a pretty montage of the first and second films in a platform-style 3Dness. Aw. End of an era this film is.