Following in the soggy footsteps of Way of Water, in Avatar’s third instalment the Na’vi are Na’viing the sky people are back again again, and Eywa continues to move in mysterious ways. But who will win the penultimate-but-one battle for the future of Pandora?

Director James Cameron already has two of the greatest sequels of all time under his belt in Terminator 2 and Aliens. Both stepped up the scale while providing a new twist on what people loved about the originals. This is his first attempt a threequel, though Avatar 2 and 3 were conceived as a single movie, and the fact they were split alone shows the huge leap in scale. But now the arc has reached its end, it’s apparent that the story this marvellous world was built for was really completed in part 1, and the additional six-and-a-half hours on Pandora has been little more than a vastly extended retelling.

Like Way of Water, Fire and Ash is high on plot details but light on story. Numerous characters and subplots unfold around familiar beats, but are of little consequence other than to trick us into thinking we’re watching something new, and provide enough padding to justify the outlandish, spectacular finale.

Once again Jake Sully brings destruction on all he meets, like a futuristic Frank Spencer. Not content with his presence nearly destroying the Metkayina clan and losing one of his children, he is now intent on arming the peaceful Na’vi with automatic weapons, and concocts a hare-brained scheme to flee with his family, leading to a disaster to rival the Hindenburg. Maybe in part 4 he will introduce measles to Pandora.

A core problem with Avatar is that its characters have never matched the grand aspirations of its visuals. The greatest epics from Lawrence of Arabia to The Lord of the Rings are not just eyeball fodder, they’re heartstring-yankers too. But outside of Avatar’s dazzling action sequences it’s rare to feel anything at all. It’s not that the film isn’t full of emotionally-significant moments for the characters; and their meticulously-rendered facial expressions can’t be faulted.

The finger of blame could more fairly be directed towards the writing, from the perfunctory, cliché-ridden dialogue (“I’m dying. But first I’m going to push out this baby”) to plot developments which often make little sense if you pause to think about them for a moment. And once again there’s a serious lack of humour. Some levity is brought by Jake Champion’s plucky little human Spider, but the Na’vi are achingly earnest throughout. I’ve got news for you Mr Cameron: hippies laugh too. When every frame takes detailed planning and hundreds of hours of labour, it’s truly difficult to understand why so little attention was paid to the script.

Fire and Ash is the most violent of the three, with a high body count and frequent Na’vi on Na’vi killing. And as always its bloodlust sits uncomfortably with its eco-spirituality. But as a tool to disseminate a message of the interconnectedness of living beings and the horrors of colonialism and ecocide to the broadest possible audience, it deserves light applause. As in the Way of Water the whale-like Tulkun provide some of the film’s most interesting and unusual moments. I could happily watch a two-hour David Attenborough documentary set on Pandora with no more excitement than banshees humping. But as the Na’vi corpses pile high, it’s hard to escape the conclusion that this is more for the corneas than the cranium.