The story is decent and firm, it's not the best or the most original, but it holds through pretty well and the author does a good job at telling it. It's been almost a year since I read it, and I still get goosebumps due to the ending.
The art... let's just say some panels are better than others. There are some scenes that are decently drawn and pretty, while there are others that looked poorly done. Both Oriko and Kiriko's character designs were pretty neat; but overall, it's nothing special.
The characters are all three dimensional, with their motivations and their flaws. There is no good side nor bad side, both have their reasons for doing what they're doing. Oriko (the titular antagonist) is no saint and does many horrible things throughout the story, but with the sole purpose of the greater good (sacrificing some lives to save many more).
Tl;dr you buy and you read.
