The Greatest Manga of All Times, in my opinion.
It is the only work that dares call itself SERIOUS and actually be and stay serious all the way (Looking at you, Puck and Ishidoro from Berserk...)
Here's the thing: I believe that a manga which calls itself SERIOUS should have no such things as COMEDIC RELIEF (what the character of Puck constantly does in Berserk. And sometimes the character of Ishidoro. And sometimes others). Well, this is the one. No such thing as comedic relief here, no goofs. Thank you for that.
Also, huge thumbs up to this manga for managing to create truly powerful characters without having them break the bounds of reality.
I understand this work is not for everybody and is at the very best a cult hit, but I would definitely recommend it to anyone who is tired of the cliched battle mangas and is looking for something that is seriously serious.
You won't find any magic systems here, no characters that are the chosen ones, no demons and dragons, no dark lords who open interdimensional portals to summon undead armies, and definitely no loved characters who come back to life. See, all those things are ingredients for PLOT HOLES. But Shigurui is the one manga (sure, sure, not the only) where ordinary characters achieve extraordinary things not through magic but through real hard work and sacrifice.
For me it will always remain the greatest manga. Much respect to this masterpiece and I hope the future will bring us more samurai/ninja manga set in universes that maintain the bounds of reality (so far I've found none like this).