The film tells the story of paralyzed war vet Jack Sully (Sam Worthington) who gets conveniently swept into a top secret mission to another planet when his genius twin brother is murdered, leaving him as the only person with the biological makeup to operate the required avatar machinery needed for the job. On the planet of Pandora, a species known as the Na'vi have been recently infiltrated by the human race. In an attempt to meld cultures, the humans create Na'vi bodies for themselves to virtually inhabit in order to better interact with the natives, a tribal society of nature loving warriors with an infinite connection to their home planet. The reckless Jack somehow manages to draw the attention of Na'vi princess Neytiri (Zoe Saldana) and become accepted into the tribe. Eventually the humans' strictly commercial interests conflict with the Na'vi way of life and Jack must choose between his species and the new family he has discovered.
With a script more careful to overexplain made up traditions and languages than to make any sort of rational sense, Avatar plays like a very indulgent space fable designed by people with too much heart and not enough brains. Moreover, it's a very grotesquely simplified feature which pins the ultra pure and innocent native Na'vi against a vision of humanity so outrageously exaggerated and cartoonish that somehow an easy target such as American corporate greed somehow manages to not get a fair shake in this mess. Sigourney Weaver plays Grace, a rare good-hearted human who runs the scientific portion of the avatar program. Meanwhile, actors Giovanni Ribisi and Stephen Lang accept the task of playing an executive and a colonel respectively who are each so disgusting as to commit genocide without a thought. These are not nuanced, complex characters. Neither are the Na'vi in most respects. Certainly, Cameron crafted a very specific history and world for them to inhabit but they are largely interchangeable, dull and lacking motivation. There's no clear moment where Neytiri falls for Jack. She just does. In a montage. Because she's the female character in the movie and that's what the female characters does. Jack too is a bit of a blank slate who makes radical life choices on a near whim and then fights to the death in a battle that comes too late to really matter.
For all the fine craft of Cameron's visual wonderland, this is a clunky overlong narrative burdened by poor writing and a preachy tone so bombarding as to irritate even apolitical ears. Viewers may still find it worth the experience to witness what Cameron has done, but anyone expecting an effective and well-composed feature will be sadly disappointed.