I really loved the series, and felt it a worthy successor to the original. Some of the art style shifts bugged me, but I figured I'm nitpicking it too much and enjoyed the show.
What did bug me, however, is that ti looks like the backgrounds, while all gorgeous watercolors and line drawings (depending on organic or humanmade, I noticed), were far less detailed and breathtaking the last shows, like the art department took a budget hit and the backgrounds suffered.
I still love it for the story, the characters, and Pabu and Bolin.
(I'm more a graphics artist than musician now, incase you can't tell...)