It is shorter, slightly less dependent on special effects, comes with vampire mermaids, and a story that can almost be explained. Almost.

By those standards, this fourth in the US$3 billion ($3.8 billion)-earning franchise first inspired by a Disneyland ride should be an improvement on the incomprehensible third.

It has also jettisoned Keira Knightley and Orlando Bloom as Johnny Depp's pouting shipmates - surely another improvement - made his loopy Captain Jack Sparrow the centre of the story, and given him his own romantic foil in Penelope Cruz's feisty buccaneer-ette Angelica.

She may be the daughter of Blackbeard, "the pirate that the other pirates fear" - Ian McShane, whose glowering menace helps restore some pirate mojo.

On Stranger Tides has also promoted Sparrow's old arch-enemy Captain Barbossa (Geoffrey Rush) from ghost to a flesh and blood - and powder-wigged - ruthless privateer in the service of King George. We get to meet his baby-faced majesty at the start in London, where Sparrow, after being invited to tea at the palace does a Three Musketeers to escape, stops in at a pub for some fatherly advice (from Keith Richards in another cameo), and discovers that old flame Angelica is using his name to recruit a crew (while we discover that Cruz looks oddly attractive in a moustache). She and her dear papa want to join the race to the Fountain of Youth.

Yes, the Spanish have finally heard back from their New World conquistador Ponce de Leon of 200 years earlier about the magical spring. And with its rambunctious start, Pirates 4 starts out feeling like a franchise revived.

So yes, a promising start and improvements all round.

But as the adventures rolls on across the Atlantic and into the jungle, there slowly comes a sinking feeling.

And by the end it seems that this chapter, though half an hour shorter than its predecessors, is still half an hour too long.

Like parts two and three, it too becomes burdened with leaden scenes that take a long time to go nowhere.

Case in point, there's a Russian roulette scene designed to encourage Sparrow to take flight off a cliff into a river below. Revolvers not invented yet? No problem. Let's use six single-shot flintlock pistols. It takes ages. You're big bad Blackbeard. Couldn't you just shove him?

Elsewhere, it doesn't help that the film's comedy factor is wholly dependent on Sparrow's quirks, rather than, well, comedy, with the pay-off of a decent punchline. There just aren't enough, though the one "make note of that man's bravery" was an amusing and blessed relief near the end.

And while Depp and Cruz supply a slight sizzle, the script has taken out some romantic subplot insurance with hunky earnest priest (Sam Claflin), who we first meet tethered to Blackbeard's mast for reasons unknown, and captured mermaid Syrena (the pale and willowy Astrid Berges-Frisbey).

They might be the surrogate Knightley and Bloom of this one. But her tail isn't the only thing that's fishy here. Given that the the mermaids are part supermodel and part piranha, this little sideshow feels like a high-tide Twilight. Actually the attack of her fellow mermaids is the satisfyingly scariest thing here - and the reason that this one might be a bit much for pre-teens - though their dresscode remains discreet.

That mermaid encounter might be memorable, but like much of the action choreographed by director Rob Marshall (who has taken over from Gore Verbinski after directing musicals Chicago and Nine) it takes place in the dark, rendered even dimmer in 3D.

While there's plenty of mass clashing of cutlery throughout, there's not one decent single swordfight in evidence here. And apart from the occasional cutlass threatening to poke you in the eye, it's not much of a 3D flick either.

Otherwise, as the fourth Pirates flick, yes, it's an improvement. But not much of one.

Stars: 3/5
Cast: Johnny Depp, Penelope Cruz, Geoffrey Rush, Ian McShane Director: Rob Marshall
Running Time: 137 mins
Rating: M (violence and fantasy horror)
Verdict: Slightly more wind its in sails, but still drifting off course

- TimeOut