In the 1980s and ’90s, director-writer James Cameron made a series of outstanding science fiction films, all of which broke new ground in special effects and as stories. In Aliens and Terminator 2 — Judgment Day, Cameron invented a new kind of action hero — a tough, hard-muscled woman with a child in one hand and a gun in the other.

But then came his Titanic. It succeeded wildly, presumably thanks to its extraordinary special effects, strong performances by a perfectly chosen cast, and the way its romantic storyline appealed to a new generation of young film-goers.

Avatar, his first film in more than a decade, is even more impressive as a technical achievement. Indeed, there has never been anything like it in terms of the way it combines computer animation with live action and the very latest in 3D technology. Moreover, there is visionary brilliance worthy of a Walt Disney in the way it imagines a new world. However, as storytelling it is stunningly unoriginal and unimaginative — pure Hollywood hack work with lashings of sanctimony and some attempts at political parable that reveal a filmmaker with all the knowledge and insight of a self-righteous 12-year-old. Cameron has essentially shifted Dances with Wolves to space and made that film’s message about white colonialism and noble savages living in harmony with nature even more heavy-handed.

The good guys are a tribe who call themselves “the People”, like Kevin Costner’s Sioux, who apologise to the animals they kill, listen to their ancestors’ voices in the trees and so on. The bad guys are not the US Cavalry this time but Earthlings, as represented by nasty, crew-cut American marines and mercenaries in the service of an evil environment-despoiling energy corporation.

Frequent filmgoers will notice additional plot elements taken from movies like Last of the Mohicans and Pocahontas, and then in the battle scenes, bits lifted wholesale from films like Full Metal Jacket (murderous marine helicopter-door gunner yelling “Get Some!”).

The stunning effects can't make up for Cameron's clunky screenplay

The hero, Jake Sully (played by Australian actor Sam Worthington), is a paraplegic marine who in the year 2154 is assigned to the grey human mining colony on a gorgeous green virgin planet called Pandora, which is the only source of a super-valuable element called “unobtanium” that can solve Earth’s energy crisis.

The planet is basically all rainforest with a more or less toxic atmosphere (consistency is not an Avatar strong suit), and cool, brightly coloured flora and fauna, including big, scary predators. It is also the home of the Na’vi, 12 ft tall, blue humanoids with tails.

The Na’vi have the elongated, almost sexless proportions of human supermodels. Some of them have attractive scarification and tattoos, and they wear their hair in corn-rows and Mohican cuts like upper-middle class girls rebelling against the system at fancy universities. But there is nothing too threatening or alien about their tribal chic, no bones through noses or penis gourds.

To move around the planet and deal with the natives more easily, the humans have created the avatar programme, whereby they grow bodies that combine human and Na’vi DNA and then download a human being’s consciousness into the Na’vi body.

Jake is downloaded into a body originally designed for his deceased twin brother and sent out to infiltrate the Na’vi. Naturally this new body is as handsome as a human one, and naturally the first blue humanoid he meets is the beautiful princess Neytiri. They save each others lives and soon, revelling in the use of his legs, Sully is learning the Na’vi away alongside Neytiri.

But the humans, and especially the evil mining executive and bigoted marine colonel, want to destroy the Na’vi’s hunter-gatherer idyll. And Sully, along with curmudgeonly scientist Sigourney Weaver and marine pilot Michelle Rodriguez, realises that the only way to stop the destruction of all the interlinked life on Pandora, is to lead the Na’vi in a desperate, heroic battle against the humans with their helicopter gunships and missiles.

The 3D technology beats even that of Up. However, it is much more effective in the live-action scenes featuring human beings than in the computer animated ones. And the strange thing is that, even though this 3D technology is so superior to previous types, you still get used to it with surprising speed.

Earlier 3D filmmakers used to deal with this by making the audience jump: darting a shark or thrusting a spear point at them out of the screen. To his credit, Cameron largely refrains from doing this. But this uncharacteristic restraint backfires — you realise all too soon just how little this clever, fabulously expensive technology actually adds to the film-going experience.

As time drags on — and it does — neither the techno-gimmickry nor the stunning landscapes can make up for Cameron’s clunky screenplay. You can almost feel him losing confidence in his writing as he increasingly resorts to a voice-over narration in the middle of the film. And in the end Avatar reveals itself as a gleaming example of what it condemns, and of Hollywood hypocrisy. For all the new-agey nature talk, it is all “shock and awe” — a soulless, bombastic, high-tech attack on soulless technology.