Captains Sao Feng (left) and Jack Sparrow in Pirates of the Caribbean: At World's End'. - Contributed

It's way too long and massively convoluted and ultimately just plain silly. Still, Pirates of the Caribbean: At World's End is a lot of fun a lot of the time.

The third movie in the freakishly successful Pirates franchise feels substantial, looks impressive and fulfils the hype surrounding it in a way the other thirds - Spidey and Shrek - haven't so far.

Having said that, it is, of course, a giant meandering mess that leaves you feeling as if you've been tossed about on the high seas for three hours, but theoretically that's also part of the allure of these movies. Director Gore Verbinski and writers Ted Elliott and Terry Rossio return with even bigger helpings of special effects, including an interminable climax in which the Black Pearl and the Flying Dutchman battle each other in the driving rain, while circling along the edge of a swirling, sucking maelstrom.

And yet, within such sequences, there are enough individual 'wow' moments that make you appreciate just how inventive and complicated an achievement this was. Stuff gets blown up (this is a Jerry Bruckheimer production, after all) and it looks like real stuff really getting blown up, not just digital blips that have been manipulated by hundreds of people sitting in the dark in front of computer screens. Though CGI technology clearly was used often, At World's End never appears fakey-cartoony, as so many of these epics often do.

As for the plot - not that it ever matters - this one's more confusing than ever. Will Turner (Orlando Bloom), Elizabeth Swann (Keira Knightley) and Captain Barbossa (Geoffrey Rush) must rescue Jack Sparrow (Johnny Depp) from the purgatory of Davy Jones's locker, where he wound up, last year at the end of Dead Man's Chest. They also must round up the Nine Lords of the Brethren Court, sort of a U.N. of unsavoury behaviour, in the hopes that their combined power can stop the Machiavellian Lord Cutler Beckett (Tom Hollander), head of the East India Co., from ridding the world of pirates.

All of these people end up double-crossing one another at some point and if you stopped to think about whether it all makes sense, it would make your head spin.

Will also wants to free his father, Bootstrap Bill (Stellan Skarsgard, still covered in barnacles), from the ghost ship, the Flying Dutchman, which Beckett controls. At the same time, Davy Jones (Bill Nighy, still covered in tentacles) wants to get his heart back, which is trapped inside a chest, which Beckett's goons control. And Willand Elizabeth must win each other's hearts back after various romantic stops and starts.

Along for the ride once again are the sorceress, Tia Dalma (Naomie Harris); wacky, bickering sidekicks Pintel (Lee Arenberg) and Raghetti (Mackenzie Crook); and a new partner, Chinese pirate Captain Sao Feng (Chow Yun-Fat), who reluctantly provides the charts, ship and crew that will help the good guys find Jack.

The first time Depp appears, in a wonderfully surreal, strikingly sparse scene, in which he's stuck in the desert with his ship, he's hallucinating dozens of versions of himself, like a moment out of Being John Malkovich. All of Depp's range is right there on display: he's goofy, proud, brazen, sometimes fearful, but always riveting.

Knightley also gets to come into her own - not that Elizabeth was ever a traditional damsel in distress - but here she evolves from feisty fighter to a woman of real confidence and power. The Pirates movies may seem like a man's world by definition, but this time there's a strong message for girls and young women as well.