I liked it.
So after my busy weekend I finished Avatar: the Last Airbender tonight. After rather vast experience with japanese animated media, it was a bit jarring to switch to a show written for my native tongue. First experiences were meh. The first season is very samey, and while the story was interesting and well told it was preachy, the characters were fairly one-dimensional, if well-written and justified, and the plot tends to explain to you where you're going once and then head off whether or not you're paying attention. The first season also contained an amusing logical screw up, in episode 9, the protagonists steal a scroll from some pirates and head back to their camp upstream. The pirates pursue them upstream in their ship. After some shenanigans, our heroes steal the ship and sail back downstream, where they encounter a waterfall. On the river that the ship just sailed up.
However, starting at the end of the first season and continuing through the second and third, characters become considerably more dynamic. The preaching continues, but I found it growing on me, after all, this is a childrens' show. And I found that not only was the preaching well-worked around, it was also preaching that I'd be happy to have my kids believe in. The show has a very strong anti-sexist message, with the number of badass girls in the recurring cast nearly doubling the number of boys, and numbers do not equate to lesser individual ability either, with Azula being the most powerful young character for most of the series, with Ty Lee, Toph and Katara being close behind her. The show also does its best to explain how even the kids without magical powers are just as special and valuable to the team.
The series could be said to be influenced by asian style, and the martial arts influence is fairly plain to see, with much discussion of discipline and hard work. However, the treatment of eastern philosophies is not entirely fair, I felt the treatment of buddhist "attachment" seemed a little unfair (though I acknowledge my own lack of familiarity with it) and there was a lack of Taoist philosophy, though the main character, Aang, is played fairly straight as being a tibetan monk.
I personally found the character of Zuko to be the most interesting to watch, but I am a big fan of watching long involved character arcs (hopefully that's not too much of a spoiler for you), and indeed found the writing clever enough to make me laugh out loud every episode or two, and hold my interest, despite the simplicity of the plotline.
I recommend the series, especially for those looking for something a little different, but familiar and well-executed. Also, be sure to have enough of an inner child that you go "that was awesome!" whenever people start throwing fireballs, tornadoes, waves or giant blocks of rock at each other.