I intend to watch it. I like the cartoon. It was a shame they had to give up their name to James Cameron's movie, which frankly did not depend on the word "Avatar".
Avatar: the Last Airbender is about a young boy named Aang who is the latest incarnation of the Avatar, a person capable of controlling all four elements. Aang was born an Airbender. In order to prevent the Avatar from incarnating, the Fire Nation exterminated the Air nation, so in addition to being the Avatar, Aang is the last airbender as well. A bender is one who can control an element, such as Earth, Air, Water, or Fire. The series lasted three seasons, and was done as a multi-year novel (rather like Babylon 5, in that respect). The Avatar has not been seen for a long time; the last Avatar, a firebender, died saving the Fire Lord (emperor of the Fire Nation). His/her (sometimes the Avatar is a woman) function is to maintain harmony between the four tribes. In the Avatar's absence, the Fire Nation has become ambitious, and the current Fire Lord desires to conquer the entire world, eliminating the benders of other nations and enslaving their people.
The TV series chronicles Aang's quest to figure out who he is, learn how to control the other elements, and rally support among the people so that they rise up against the Fire Nation and restore the balance.
My biggest worry about the movie is that there's a hell of a lot of material to cover, and I haven't the slightest idea of how they can jam it all into a single feature-length movie. As my husband said, "Maybe if it's Part 1 of 47."

Maybe it's basically just the ending. That could work, though you'd lose a lot from the major character arcs.