Many "fans" are in unreasonable denial of this fact and continue to think A:TLA is simplistic.
The cartoon series is made by American cartoonists, despite the Japanese Anime touch.
The story is an epic adventure in which a group of humans with the ability to bend the individual substances of the Earth travel around the world in an effort to teach the Avatar how to manipulate them. These substances are Water, Earth, Fire, and Air. The Avatar is a spiritual being reincarnated repetitively from body to body. It exists to aid humans in their suffering and to bring tranquility to the Earth.
The Avatar in this story is a young 12-year old boy named Aang, who comes from the Air Temples of the Air Nomads. He runs away when he finds out that he's the Avatar and coincidentally escapes in time before Firelord Sozin (king of the Fire Nation) torches the temples with a comet in an effort to destroy Aang, who would supposedly end his attempts to conquer the Earth Kingdom.
When Aang runs away on his pet sky bison, he falls into the ocean due to a storm. Overpowered by the churning waves, he sinks below the water and the Avatar state (a condition in which the Avatar combines all his/her past experience with the experience of the other Avatars into one, becoming stronger than before) caused the water to freeze, preserving him in ice.
Aang learns how to control the elements from these teachers and also finds out how to master the Avatar state and to remove people's bending.
Aang confronts the Firelord at last, and eventually traps him in the embrace of the Earth. Then, he removes the Firelord's ability to firebend, refusing to kill him because of what he learned from the monks he grew up with in the Air Temples. Then Ozai is sent to jail for the rest of his life.
Avatar: The Last Airbender
The show is often thought to be anime,because the art style,even though the art style is Korean.The show's story style is a mixture of asian cultres,mostly Chinese.
Basically,the story is about a world where people can "bend" the 4 elements which separates the land in 4 nations:
They were all living together in harmony.
However,everything changed when the Fire Nation attacked.
Only the Avatar,who can bend all 4 elements could have defeated the Fire Nation.But when the world needed him most,he vanished.
Hundred years have passed since.
Two 14 year old brother and sister,Sokka and Katara,have found a massive iceberg,which creates a giant ray of light,when Katara cracks it open.(The light signals Zuko,a Fire Nation warrior who is in a search to find the Avatar.)
Inside they find a boy with a flying bison.The boy turns out to be an airbender.
After the three returns to the South Water Tribe,Katara and Aang go penguin-sleding,stumbling into a Fire Navy ship.
Upon going into the ship Aang realizes he has been frozen in the iceberg for 100 years (the entire war)Later Aang aciddentally activates a booby trap,which signals Zuko.Later,Zuko comes to the South Water Tribe and asks Aang if he is the avatar.Since there is no other airbenders,the question is obviously yes.
Katara,Sokka and Aang's flying bison Appa manage to heelp Aang escape.
TL;DR : The show is THE shit.It's one of the rare things that you can watch on Nick without getting a headache.It's totally worth watching and has a perfect storyline and a great mix between Romance,Action and Comedy.
Sadly it got ruined by a 2010 movie adaptation which includes horrible actors,horrible (the actors don't even match the characters)acting,whitewashing(the Fire Nation,who were the whitest in the movie,are indian,while Sokka and Katara ,who are a bit brown,are completely white).Also they missed an enormous ammount of Key-episodes,which are important to the later episodes (The sequel thankfully isn't going to be produced).Did I mention the production budget was 150 million dollars ,which is only 50 million less than Cameron's TITANIC!!!!!
"Water. Earth. Fire. Air. Long ago, the four nations lived together in harmony. Then, everything changed when the Fire Nation attacked. Only the Avatar, master of all four elements, could stop them, but when the world needed him most, he vanished. A hundred years passed and my brother and I discovered the new Avatar, an airbender named Aang. And although his airbending skills are great, he has a lot to learn before he's ready to save anyone. But I believe Aang can save the world."
-Katara,Avatar : The Last Airbender Opening sequence
Interesting facts to know about Avatar is that:
1. Most Avatar fans hate and bash on Anime, yet they dont even realize that they ARE watching a show that is mostly Anime itself.
2.Avatar is watched mostly by canadian fags that have no life whatsoever, and would love to meet and fuck Katara/Aang in real life.
3.Avatar is Animes BITCH. Without Anime Avatar would be another gay TV show for kids.