Late to the party, but yeah. It's really, really good. If you haven't seen it, you should. It's available on Netflix (streaming, even), and yes, it's 30-some hours total, but I think it's worth the time.
The thing is, even though it's "a kid's show", there's no skimping on storytelling, and the creators give the audience credit for being smart and well-read. A lot of credit. Here's an example from the final episode:
In the final series of battles, there were a bunch of interesting things going on with the score. Lots of moods other than just 'dramatic'. And during the battle between Aang and Firelord Ozai, when Aang goes all avatar-mode? It sounds a hell of a lot like Koyaanisqatsi, by Philip Glass. And "koyaanisqatsi" means "life out of balance". Which is a really interesting non-verbal commentary on what's going on with the story at that point. And I don't think that's at all accidental.
So yeah. For kids, but not only for kids.