Avatar - Jake Sully (Sam Worthington), in his avatar form, learns the ways of the Na’vi from Neytiri (Zoe Saldana)

So Avatar, James Cameron’s much hyped, reportedly groundbreaking 3D sci-fi epic, has finally reached the big screen. What has Cameron been up to in the dozen years since Titanic? What has he spent upwards of $240 million creating? And does the 3D give you a headache?

The last bit is easy. No, it doesn’t, at least as far as I was concerned. For me, watching the movie was eye popping without being eye aching, and as immersive an experience as Cameron has been promising – which probably goes some way to answering those other questions. Cameron has been spending time and money getting the technology right.

He’s also been spending an awful lot of time cooking up an elaborate sci-fi adventure story that will delight many but repel others – how this particular equation works out will determine just how big a blockbuster the movie turns out to be. My guess is that the box-office take will be huge but not Titanic.

As for that elaborate story, well it’s set in 2154, 145 years into the future. In the intervening years, humanity has apparently trashed our planet (it took us that long?) and the only solution to Earth’s catastrophic energy crisis is a rare mineral called unobtanium (dig the name) that is found on a distant planet (actually a moon) called Pandora.

Avatar - James Cameron’s epic sci-fi adventure

A rapacious corporation, backed by a private army, is exploiting the mineral, but Pandora’s hostile environment and its understandably disgruntled indigenous people, the Na’vi, are slowing things down. To get around these obstacles, the corporation has created a number of genetically engineered human-Na’vi hybrids, or avatars, that can withstand the planet’s toxic atmosphere.

These avatars resemble the Na’vi themselves – 10-feet-tall humanoids with blue-skin and a long tail – but they are remotely controlled by individual human drivers who share part of the avatar’s unique DNA and can plug themselves from a distance into the avatar’s consciousness.

Avatar - Jake Sully (Sam Worthington) encounters his avatar in James Cameron’s sci-fi adventure

Sam Worthington’s paraplegic ex-marine, Jake Sully, is one of the drivers, chosen because he shares his genetic makeup with his recently deceased boffin twin brother. The scientist who runs the avatar programme, Sigourney Weaver’s Grace Augustine, is none too pleased to have a ‘jarhead dropout’ on board her team, but when Jake inhabits his avatar for the first time, he is thrilled to regain the virtual use of his legs.

Jake’s first venture into the jungles of Pandora, however, sees him get stranded and left behind by his colleagues. No one expects him to survive the night, but he’s rescued by a beautiful Na’vi female, Neytiri (Zoe Saldana), and she introduces him to her clan, whose home is right on top of the planet’s richest seam of unobtanium.

Avatar - Neytiri (Zoe Saldana)

The corporation, and its gung-ho head of security, Colonel Miles Quaritch (Stephen Lang), are delighted to have an inside man to help expedite their plan to remove the Na’vi from their land, but as Jake spends longer with the clan and learns their ways and skills he goes increasingly native.

Watching Jake’s journey through our 3D glasses, we’re with him every step of the way, so that by the time of the film’s climactic battle we’re all rooting for the blue-skinned aliens to prevail against the greedy, warlike humans.

Scratch beneath the blue skin and you see that Cameron has created a sci-fi allegory of the USA’s bellicose treatment of indigenous peoples down the ages – from the Native Americans to the Vietnamese and beyond. (Insert other colonial oppressors and aboriginal victims, as you prefer.)

Avatar - James Cameron’s epic sci-fi adventure

Audiences won’t be going to Avatar for its political subtext, however, or for its ecological warnings or Gaia-like spiritual leanings. They’ll be going for its virtual-reality thrills.  Fortunately, Cameron really does deliver. The 3D is more involving than anything I’ve previously encountered – and not because Cameron is continually thrusting objects in our faces. The effect that impressed me the most was the sensation of things moving towards the screen rather than out from it.

The film’s most-breathtaking moments, for me, weren’t the soaring rides on dragon-like winged creatures or the vertiginous climbs up the sides of floating mountains (nicked from 1970s Roger Dean album covers, surely), exciting though they undoubtedly are. No, what wowed me the most was seeing wispy floating seeds drift past my ear and sail away from me, leaving me with the feeling that I was deep in the heart of Pandora’s lush jungles – and of Cameron’s imagination.

On general release from 17th December.

[swf]http://uk.player.filmtrailer.com/v3.1/&mid=2845&channel_user_id=441100180-1&repeat=1&volume=0[/swf]

To activate the sound in the trailer: hold your cursor over the screen to reveal the control panel and click on the volume control in the bottom right-hand corner.