I have an unholy love for cartoons and never really grew out of the Saturday morning thing. This is the absolute best American animated series I have ever seen. The only other series that is on par is Samurai Jack. Actually, there are a lot of great anime series but these two are the best produced outside of Japan.
Back to Avatar. Three well-written, beautifully animated seasons that reached audiences well outside of it’s 9-11 year old demographic. It is set in an Asian influenced world where four nations practise martial arts and bending their respective elements.
Be careful, you will sit down to watch only an episode or two and end up watching a whole season.