This is one of those stories that capture you completely. It starts like a simple story, and then the climax grows and grows. I read 25 chapters in two days -- I could not stop. The only bad thing about it is that it's ongoing, and now that I read all the available chapters I feel like I'm in withdrawal. Amazing story, living characters. The mangaka is creating a masterwork. My hope is that she will treat her characters well to the very end.
Another aspect that I find amazing is that the elements of the story match perfectly with what I have been reading in "serious" books about Japan's history and philosophy. In particular, the concept of the "impure" that is used in the manga is historically faithful; personally I find this great, as it makes it even easier for the reader to "surrender themselves to the story" and embrace a voluntary suspension of disbelief.