Grade: C

It isn’t all that unusual for a sci-fi movie to be a space-age clone of a western—“Star Trek,” after all, was originally sold as an update of “Wagon Train,” and there’s plenty of the Old West in “Star Wars,” too. So one shouldn’t be taken aback by the fact that James Cameron’s “Avatar” is basically “Dances With Wolves” in outer space. Of course, there has to be a futuristic twist to the tale of the military man who “goes native” when he becomes enamoured of the noble savages he’s been sent out to fight.

So here Jake Sully (Sam Worthington), the wheelchair-bound Marine tasked with reconnoitering the Na’vi, a tribe of ten-foot, azure blue creatures that inhabit a tree on the planet Pandora that just happens to sit atop a vast deposit of a mineral the earthlings are anxious to extract, is transformed by the miracle of modern genetics to look like one of them. That’s an old story, too: anyone who remembers the episode from the original “Outer Limits” series titled “The Chameleon” (written by Robert Towne, and starring Robert Duvall) will find it familiar.

Of course, just because a narrative is derivative doesn’t necessarily make it awful. But Cameron’s take on this one is pretty puerile. The company that’s out to despoil the Na’vi’s territory—of a mineral that’s actually referred to as unobtainium!—is led by a greedy yuppie named Selfridge (think Selfish), and is played as a slimy profit-pusher by Giovanni Ribisi; and his security chief, a colonel named Quaritch (isn’t that rich), is portrayed as a snarling martinet by Stephen Lang. There are, of course, a few folk with some humanity left in them who side with Sully when he sympathizes with the Na’vi: Grace (Sigourney Weaver), the hard-nosed yet conciliatory inventor of the apparatus that converts Jake into one of Them; Trudy (Michelle Rodriguez), a crack pilot with knew his brother; and Norm (Joel David Moore), a geeky but good-natured scientist.

But it’s the Na’vi themselves that are most important to the effort against the firm. They’re portrayed as a sort of extraterrestrial Indian tribe that worship the planet goddess Eywa (just think of Mother Nature) and can commune with plants and animals in their local habitat by plugging their super-sensitive tails into them. They also have a rite of passage that consists of bonding with a giant flying dino-thing that becomes one’s mount by a kind of Vulcan-like mind-meld. The transformed Jake’s greatest champion among them is the beauteous Neytiri (Zoe Saldana), who saves him from being eaten by a local beast, becomes his tour guide and eventual love interest, and encourages her comrades to accept him as one of them against the initial resistance of the male warriors led by Tsu’tey (Laz Alonso).

But Jake and his few human allies prove their mettle when Quaritch launches a massive attack on the Na’vi Tree and they join the tribe, and the other clans, in its defense. The finale is a huge, climactic battle featuring bombers, helo-fighters, lumbering robo-cop-like suits, those flying dino-birds, Na’vi “horsemen,” and some creatures resembling rhinos, as well as lots of other critters and military paraphernalia.

It’s certainly a spectacular sequence, even if so overlong and effects-packed as to be exhausting, and it’s enhanced by the use of 3D, which also gives the shimmering alien CGI landscape of Pandora a gossamer quality that’s very impressive without resorting to the coarse in-your-face cliches the technique invites. And it’s undeniable that the advanced motion-capture technology that Cameron spearheaded to bring the Na’vi to life is a formidable accomplishment, not only achieving a smoothness of movement new to the format but allowing the faces an expressiveness that’s a real breakthrough.

But the technical wizardry is at the service of a recycled plot and a script rife with cardboard characters, human and alien both, and dialogue that sounds as though it had been lifted from the pages of a third-rate comic book. The issue with “Avatar” is simply whether the visual pizzazz makes up for the mediocrity of the storytelling. For some, the fanboys in particular, the answer will be yes; but others may be far less tolerant of nearly three hours of mayhem and banality, however perfectly packaged. Appropriately, Cameron’s movie is being released for the Christmas season, because it’s like the big, gaudy present under the tree that proves to be empty when you unwrap it.