It took us a while, but we've completed this series from the DVD versions. Avatar The Last Air Bender is a TV series compiled into three "books:" Water, Earth, and Fire with each 'book' having a season's worth of episodes.
I must say I enjoyed this as much or more than my son, lol. I found the story compelling and some of the character development well done. I'm not saying this is a masterpiece by any means. I found the third 'book' to be the weakest of the series and throughout the series, much of it was predictable. Still, it was very fun to watch. I do love martial art movies and this one had a few different ones to show off. I also enjoyed the humour woven into the shows (beyond the punny or slap stick parts).
This is an *American* series and not Japanese animation and implements different Asian concepts.
An overly simplified summary from IMDB, "In a war-torn world of elemental magic, a young boy reawakens to undertake a dangerous mystic quest to fulfill his destiny as the Avatar." Follow the IMDB link for more info and some video clips.
Avatar wiki, a place to learn even more about the series and it's characters.