The concept centers around humans on a planet named Pandora, a gigantic wilderness. inhabited by giant pterosaurs, reptilian wild dogs and shovel-headed triceratops. The air on the planet is unbreathable by humans, but the planet carries huge deposits of 'unobtainium', which is worth a fortune for some reason. The mining colony on the planet is policed by Marines on hire, and all activities require gas masks. The people here are at a big disadvantage from Pandora's natives, the Na'vi, who can breathe the air and telepathically tame its various beasts, are 15 feet tall and super-agile and live on a gigantic tree. To facilitate negotiations and understanding (A euphemism for "get them off their land as there's a deposit on it"), a team of scientists figure out a way to project their consciousness remotely on Na'vi bodies genetically engineered for the process. These are the 'Avatars', of whom newcomer Jake Sully (Sam Worthington) and Dr. Augutine (Sigourney Weaver) are of note. Sully volunteers for the process as he's a cripple in real life, and upon waking in his Avatar, finds himself mobile and in a rush. He then has himself an accident and gets lost in the forest and runs into the daughter of the Na'vi chief.
It took about half an hour to come up with the above summary, which speaks volumes about the detail and texture of this world Cameron created. From Avatar-Sully's meeting with the daughter (why a daughter and never a son?) though, the movie proceeds on a course easily visible to anyone who's ever watched a movie. She trains him in the ways of the Force.. sorry Eywha, they fall visibly (note the use of the word) in love, he tames a giant flying beast and eventually sympathises enough with the natives to defend them against the evil corporation and eviler mercenary Marine. They have them some amazing battles, and in the end, the evil Empire (the Merchant-Military one) is defeated and Sully transitions permanently into Avatar-Sully, setting the stage for a sequel.
The 3D thing that Cameron pulled off is amazing, as is the detail put to the world of Pandora. In that respect this movie is a milestone ushering in a new style of movie making, the way Superman ushered in special effects, Star Wars brought in space opera and Titanic opened up squealing teenage girls as a viable fanbase. It's also to Cameron's credit that despite all the flaws of the second half, one is riveted to the screen till the end credits roll. But on the count of stortelling, Cameron seems to distance his present work from his previous work of the 80's and 90's, wherein explosions and special effects were only the cherry on top to well-defined character sketches and a rock-solid story.
Verdict: A Must See, but could have been far better