Hard to give the opinion on this manga because not only it had the original concept story (vengeance using proxy agent), but it also had a unique main character, and realistic story overall, but at the same time, it is not targeted to the mainstream audience in the way that the story being told was too "deep" to some of people that can be labelled as boring or non make any sense at all.
I do find this manga is very intriguing to read. A lot of psycho babble in this manga that actually does make sense if you think about it, and it's true when you apply that sort of thing in the real world.
This manga really doesn't hold any punches, it tells the story as it is...it doesn't shield a particular character from plot armor. Every character you see in this manga have some sort of flaw, and there's no such thing as a black and white / good vs evil setting , only grey area.
If you are not in the right mindset, and doesn't like to think things a lot, then probably you don't like this manga. But if you are like me... you have to read it.
Probably one of the best seinen manga I have ever read. Trully embodied what its like to be in "seinen" genre.