Most of the emphasis of this show is put on the rule of cool. The action looks great and the atmosphere is filled with testosterone, even when it comes to the women, well, some of them. The choice this anime makes however is to have very few information scarcely scattered between action. The way the characters and setting are provided with details is by first teasing some information in episode x, the presenting half of it in episode x+1, and then gradually adding more and more to it in the following episodes. This rule has been consistent from episode one until the last and is extremely inefficient. It was predictable that it won't have any chance to have a good ending. Instead the teasing continued until the end and viewers felt cheated.
However the way it ends is not the only way we can talk about quality in a show. There are some clear ques of why the writing for this one is rather poor:
1. the setting is complex and confusing. There's a vast number of characters but none are properly presented aside from the two main characters. The clans will play a big role in the plot but having such poorly defined characters will end up leading to a confusing plot where you don't know why X character does Y thing, and if you did it would probably make little sense.
2. information is being obfuscated. Some is teased but never given. Some is teased and gradually and inefficiently given away.
3. there's too many things happening at the same time. Pacing ends up being unbearably slow. Plot becomes confusing.
4. there's too many flashbacks and they are inefficient. This also ends up hurting the pacing.
All in all, the main reasons for why this anime is bad and probably the source material as well are not just the fact that the anime ends in a horrible place, but because the writing quality is poor.
