I would say this comic is mediocre at best. I do not consider it a manga specifically but rather a comic book drawn in mangastyle since this book is read from left to right as typical for comics and not right-to –left as in mangas.
Now, I may be a tad biased here since I compare this to the movie version by M. Night Shyamalan (no idea why he still makes movies) but I think, for all its mediocrity, this comic was actually a lot better. This here actually had some true humor, intentional one, not unintentional like in the movie, and often it works a lot better in getting the tone across. In fact when the comic deviates from the Shyamalan style, which it sadly still suffers from significantly, you do see the potential for a good story coming through. To give an example: what is said usually matches what is depicted, they do not ask him way into the story what Aang's name is, they actually show some scenes of growing defiance against the domination of the Fire Nation after the Avatar resurfaced. In addition you do see the Kyoshi warriors, (but never the Firelords except as looming shadows like in the cartoon), looking different of course, and they are more than mere cameos, Katara comes along as having more guts and being useful to the story in more than exposition.
The art is ok also.
However, from the beginning onwards the story suffers from the problem of being too rushed and having a lot of plotholes regarding background and motivation. Which is one of the things where it comes close to the Shyamalan pattern and there are other cases as well, e.g. like the Earthbenders still being imprisoned on common ground and not thinking of rebelling against their few guards. However, up to 75 % into the comic these are actually the only problems. When the last quarter is reached the real problems begin, where it all falls apart. Suddenly Qi is mentioned, which was never mentioned before, Aang speaks about a Dragon Spirit as though everyone knows about that already although it never appeared before. Also general Gao just appears out of nowhere and so do several other elements, e.g. all previous artwork suggested that the Firebenders do not need existing fire but can create it themselves, but towards the end it is suddenly suggested that they cannot do so without Sozin's comit, except for great masters. Aka, towards the end it turns completely into Shyamalan's story, it partially felt as though the previous style and story was brutally hammered into the Shyamalan shape; the artwork and general constraints of the medium help a lot, there is far less telling and more showing, and more emotional impact but that could not save the story in the least.
So if you do not read this book, you missed nothing. At all. It is better than the movie, but still mediocre at best.