Gene Luen Yang delivers a fantastic script that weaves three distinct storylines into a compelling narrative. He does a good job balancing out the more serious stories of Aang's search for peace and Zuko's struggles to be King, with Toph and Sokka's sillier attempts to create a metal bending school. It can be hard working with licensed material, but Yang captures the characters' voices well and tells a story that feels right at home in the Avatar universe.
Team Gurihiru does an excellent job of converting the Avatar world to print comics. I was especially weary of reading Avatar in comics form, because so much of the show's style is about movement. The way they animate bending and fighting was amazing. Gurihiru impressed me by capturing a sense of movement fluidity, both in their art style and in the panel layouts. The art team knows when to quicken the pace and increase the action, and when to slow down and let the characters drive the story.
If you're a fan of The Last Airbender, you will love this series. Even if you're a newbie, The Promise is a very strong stand-alone book, which will probably entice you to go back and watch the original series. With only being $10.99 for 80 pages of comic, you can't really go wrong and should definitely pick it up for yourself or for your kids. It makes a great distraction while waiting for new episodes of Legend of Korra, the outstanding new show in the Avatar series.