There is a distinct difference between “Anime” and “Animation”. Both of these words bring up different images and expectations into our minds. Looking at the animation style of Avatar: The Last airbender it’s easy to classify it as an anime. Avatar, however, has a lot of aspects of it that differs from eastern anime- most of which stem from its western roots. This was one of the topics covered in one of the many panels at Anime North.
The biggest difference between eastern and western anime is the amount of preplanning and preproduction. This is the main reason you tend to have a lot flash- back inside episodes of eastern anime. They animate the new episode after the previous episode is aired, which means there isn’t always time to complete a full episode without needing something to take up the time.
Similarly, eastern anime have voice actors come in afterward to speak over the animation, whereas most western anime have the voice actors come in, say the lines, and the animators will draw in relation to those voices. The Avatar series is great because not only do they have the main speaker moving as the conversation is going, there are also movement in the background as well.
The animation style itself borrows from eastern anime, but isn’t quite the same. They animators take this a little further in the new series: the Legend of Korra, which delves further into the eastern style of animation that we are used to seeing.