Excellent take on Avatar: The Last Airbender/Legend of Korra for the Apocalypse World engine. It does a really good job of translating the setting to the rule system. My one complaint with the PDF is that it's not bookmarked, but that's a very minor issue. The formatting is pretty barebones, but it doesn't particularly need to be anything more than that. It does its job.
As far as the actual meat of the game, yeah, it absolutely does a good job. Apocalypse World is, of course, easy to tweak, but speaking from experience, keeping the balance of "engaging game" and "not too bloated" can be more difficult than one would think. This book handles it beautifully, giving me plenty to make it feel interesting and varied without weighing the sleek engine down. I also enjoy that the author was willing to step outside the box a little with the engine itself, implementing things like Oaths (which I don't think I remember being in Apocalypse World), sub-playbooks and animal companions.
Interesting side note: While it can absolutely be used for Avatar roleplaying, the sales pitch doesn't lie when it says it can be used for all sorts of other wuxia settings as well. As a fan of the Dynasty Warriors video game series, I can absolutely envision the components of Legend of the Elements emulating high-action Three Kingdoms roleplaying, for example. The only thing it's missing is rules for mass combat, but when one warrior is worth a thousand men, that's not necessarily something you need.
All in all, very pleased with the purchase. Worth the $10 US in my book.