Great, but not good
If authors set out with the intention of shitting on someone else's work and proclaiming their superiority, their spite oozes out through the cracks and ruins everything. To her credit, Vathara is an eloquent author. She has the breadth and depth of knowledge to deliver an excellent history lesson. Every action scene is a spectacular affair. Where the show couldn't expand on some detail, she used the advantage of an unrestricted word count to breathe life into features that quite plausibly could have been there. This was most apparent in the Ba Sing Se arc, where refugees and side characters and the Dai Li all had their chance to be special. They shone. It was brilliant. I disagree with her opinion that the best 'oc's are made by adapting memorable side characters from other stories, but she made it work. I can respect that. The frequent little jolt of "Hey don't I recognize that person from somewhere" was a pleasant sensation, like meeting an old friend. I didn't like the criticism of the show's 'lack of realism'. They sounded too much like complaining that Tolkien didn't spend enough time on Aragorn's tax policy, and rang utterly hollow when the solution was to make all firebenders descended from dragons or to give every nation a binding clause that grievously harms people for acting against their loyalty (fire)/rejecting family (water)/breaking a contract (earth)/abandoning a philosophy (air). 'All actions should have consequences', Vathara rails through characters and belligerent author's notes. In story, this phrase exclusively castigates Aang. The Fire Nation always has an excuse. Slaughtering the Air Nomads? They were forced to and if they tried to disobey it they'd drop dead of element sickness. Rebelling against the throne? Impossible, drop dead, element sickness. Zuko can't control his temper? It always works in his favor. Aang and the Ocean Spirit decimated an army? That was a tactical spirit nuke and now the sea is full of zombies. Vathara seems to have been personally slighted by the Avatars. She rants about them a lot. It gets tiresome. Vathara rewrites the story's background but neglects characters she hates. Aang stumbles along acting, reacting and (very) gradually learning like he's still in the show. Zuko starts off unlike the early season 2 wounded teen, gets all his character development in before Ba Sing Se, and stays the same (grumpy but perpetually justified) for the next 70 chapters. Ironically, Aang got the most natural growth. Remember the well-written side characters? They can be classified as "smart, endearing and Right" or "agrees with Aang". Everyone who sides with Aang turns out to be horribly compromised in some way which leaves a bad aftertaste. Everyone else inevitably winds up as a sounding board to tell us Zuko is awesome. Zuko is awesome. But as Embers demonstrates, awesome doesn't make a story good.
(duplicate review. please delete.)
Is well written the same as good?
The question probably sounds rather tautological and obvious but it's actually the main issue I have with the fanfic. As it stands, it is well written. The story is strong, the plot is complex but internally consistent and seems mostly free of twists pulled out of bottoms. The characterisation in the story is pretty consistent. HOWEVER. (And this is capitalised for a reason.) However... the characterisation in the story is internally consistent, but very much less so with the characters as presented in the show. The names are the same, they look pretty similar... but for me? That's really about it. Zuko in this story is treated as if he's undergone his entire canon character development, and more besides, before the time of Ba Sing Se, which canonically was when a great deal of said development actually took place. The flaws that remain are of the 'informed' variety that tend to somehow conveniently work in his favour as much as against it. Other characters (both canonical and original) are presented as being more 'realistic' versions, deconstructions almost. Which is laudable, except that everything before the story starts is meant to be the same as canon, and characterisations and personalities that I never recall seeing in the series suddenly pop up in the Embers characters. Cultural attributes and values shape the characters... attributes and values that never appeared in the show. The past of the Avatar world is made up pretty much entirely of old cloth and whatever new idea the author wants to push right now. Some of the above can be explained (or excused, if that's the term preferred) in that the canon backgrounds had not been explored in any great depth in the show. With that said, it takes a very certain type of mind to take the pacifist, Buddhist-styled Air Nomads and somehow reach the conclusion that this comes from the end result of them once being Mongol-like conquerors and imperialists. Other tribes get similar treatment. The other issue that WILL arise is that the author has characters they like, and those they don't, and even a cursory reading will make it extremely obvious which is which. At some points it can be hard not to feel that certain characters literally cannot do anything right. Whatever they do, the plot will unfold in exactly the way as to make them wrong to do it. If you like the characters the author doesn't, or don't much care for the ones they do, the seven deadly words may well be uttered. In summary, I would have to say that if this was an entirely original story with completely new characters and a setting the author had made up for themselves I would not hesitate to completely recommend it. But as a fanfic of Avatar, even an AU one? I would still probably recommend you try it, with reservations - but do not go in expecting this to be the same story and the same characters you watched in the show itself.
Embers is...well, it's certainly an interesting story. It started out life as an Avatar: The Last Airbender fanfic, but by now has diverged significantly in tone from its founding source. If you like elaborate world-building, rules about spirits, the development of culture when concepts such as justice and family are a spiritually binding force on the people, and discussions of morality, it's well worth a go. That said, the characterisation is polarizing — some people love it, believing that the characters are deepened by Vathara's use of real-world psychology in the same way the setting is improved by her use of real-world myths and geography. Others, however, find that her interpretation of the characters clashes with the sense of them they get from the show, and disagree with Vathara's take on morality and responsibility, which is a great deal harsher than the show's. Fans of Aang and Katara may want to give this one a miss; Vathara writes very well, but the flip side of that is that when she dislikes a character, it hits home hard.