First, let’s be clear… Avatar is much more than a film. It’s a prescribed cinematic experience. Pure effect. The greatest sideshow on Earth.
Cameron's aim is to take our franchise-frazzled minds and plug us back in to the mainline; to conjur the wonder of those early silent-movie audiences, aghast and alarmed as a steam-train chugged from horizon to foreground.
Like Avatar's hero, injured marine Jake Sully (Sam Worthington), he wants to blast away the past and see through new eyes.
Avatar is the new benchmark for escapist entertainment; the ultimate on-screen dream. More suspension of self than suspension of disbelief.
As Jake dives in and out of his split human/alien personalities, Cameron is equally urging us to leave our burdened minds and busy bodies behind - to sink into our seats and immerse in a virtual world.
In the febrile jungle of planet Pandora, it's a thrillingly alive world of whooping devil-monkeys, scuttling super-spiders, fluttering titan-orchids and bioluminescent air-jellyfish.
The ground is patrolled by hammerheaded, Triceratops-like behemoths and saber-toothed jaguar-giants, while immense, lizard-headed mega-birds rule the air.
But Cameron keeps us connected by not pushing the otherness into hokey, adolescent alien-sketch territory. This isn't an open-air version of the Star Wars cantina: weird for weird's sake.
It feels equally distant and familiar. Like an advanced version of our own world; as if Cameron has run the whole of the current ecosystem through some kind of evolution extrapolation software.
And into this wild and wonderful arena… Enter Avatar Jake, a hybrid of human and Na'vi - the blue-skinned, golden-eyed, oversized indigenous people.
"A marine in an Avatar body", snarls Stephen Lang's feral colonel. "That's a potent combination…"
Jake's mission: to blend with the locals and convince them to "relocate" - away from an area rich in precious/lucrative rock deposits. To go native…
Instead, he goes rogue - after being trusted and trained by Zoe Saldana's fiery Neytiri. Like Human Jake, she's a warrior, and the two bond over a spectacular battle/ambush that humbles him and ennobles her.
For Jake, it's love at first flight. As the two soar and scamper through the shimmering treetops, he revels in swapping his broken real-world form for a faster, stronger, more athletic vessel.
But, this being Cameron, there's forbidden love. Not love struggling to reach across time (Terminator) or class (Titanic), but something far more strange and affecting: interdimensional love.
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In fumbling hands, this could have badly misfired - strange and silly instead of curious and moving.
But, unlike his last film, Cameron doesn't over-season the sentiment. He drills straight through to the emotional core: his leading man's wrenching inner-space odyssey - from interloper to insider to outcast.
But the success of the human/Na'vi love-story thread is mostly down to Saldana. Her subtle, spiky performance is a delicious foil to Worthington's wide-eyed neophyte.
She might have played it haughty and aloof - and annoying. Instead, she makes Neytiri untameable and irresistible, brimming with spirit and soul - and making her, and the other CG characters, feel more weighted and real.
So, yes, some of the CG is a bit floaty and videogamey. But, blended with the extraordinary, retina-frying 3D design, it soon becomes the work of a joyless cynic to spot the joins.
Cameron has taken the techniques of 3D film above and beyond the standard jabbing and jutting gimmickery. Every frame is dripping with sumptuous foreground detail - swirling ambient debris, needle-sharp textural subtleties, multi-layered character nuances…
It's a motion picture where everything seems to move. And it's utterly captivating. A glistening banquet for the senses.
This isn't Cameron simply taking existing technology and tweaking the application to his standard.
This is the work of a master film-maker owning and reclaiming the entire concept of 3D; pushing and challenging other film-makers to keep up.
But it's also a long way from just some sterile technical exercise. Avatar sees Cameron revisit his favourite trick: using hardware to unearth humanity.
He carves out the most ambitious screen backdrop ever conceived, then uses it as a staging ground for riffs on military morality, environmental anguish, science versus nature, spirituality versus pragmatism…
And, in his hero's story, he presents a grand illusion - offering what seems to be a theme of internal conflict and physical reawakening before unleashing a final sucker-punch reveal that's unexpected, devastating, moving and instantly iconic…
Oh, yeah… And there's action, too: sinew-straining, jaw-snapping beast battles; rampaging fist-fights; arcing arrow attacks; whirring gunships peppering the canopy with incendiary fire; lumbering battle-mechs pummelling the life out of Pandora with synthetic death.
All - remember - in 3D…
So, let's be clear… Avatar is much more than a film.
It's an audacious, awe-inspiring work of modern art that reinvents and redesigns the whole process of sitting in a darkened room staring up at a screen.
Sure, it's taken him ten years, but Cameron has achieved no less than a rebirth of cinema.
Jackson, Spielberg, Fincher, PTA, Del Toro… Over to you...
Game-changing - yes. Spectacular - absolutely. Occasional dodgy dialogue and dramatic imperfections - of course. But still - wait for it… - a titanic achievement.