Vagabond

Vagabond is an epic, martial-arts, historical manga series written and illustrated by Slam Dunk creator Takehiko Inoue, which began serialization in 1998, spanning 37 volumes before going on indefinite hiatus in 2015. It has won several awards, and with over 82 million copies sold, it has become one of the best selling manga series of all time.

Plot
The series follows Shinmen Takezo, later the legendary Ronin Miyamoto Musashi, and his journey to become "invincible under the heavens" after surviving the disastrous Battle of Sekigahara.

Why It Rocks

 * 1) Absolutely incredible artwork by Inoue that clearly took lots of time and effort to do and looks absolutely beautiful because of it. Some scenes even look almost photorealistic, which is quite an achievement.
 * 2) Takezo/Musashi is a very interesting character, in that he battles many to the death not out of sadism, but to prove to himself that he can beat any challenge. He's not, however, a perfect samurai as there are plenty of people who are more capable than him and have received actual training, unlike Takezo who was simply brutalized by his vicious father. As a result of all this, he's become quite violent and antisocial, but still has a set of morals which he refuses to break and non-violent feelings that often take over.
 * 3) Plenty of likeable and well-developed characters who are actually important to the story, like Takuan Soho, a monk who's brutally honest yet sympathetic, and Jotaro (not to be confused with Jotaro Kujo) who's Musashi's first apprentice. There's also Otsu, Matahachi's ex-fiance whom Musashi develops sexual feelings for, Oko, his new fiance who was once a prostitute, and Oko's daughter Akemi who saved Takezo and Matahachi.
 * 4) Being that the real Miyamoto Musashi didn't keep a journal of his travels and journey, it offers Inoue a lot of creative freedom which he takes full advantage of. Takezo is pretty much seen as just a madman in the beginning due to his tendency to accept fighting challenges and go too far, therefore he has very few friends, and quite a few enemies in the village he grew up in. This leads him to make his decision to become a Ronin and change his name to Musashi at the behest of the sympathetic monk Soho.
 * 5) Very realistic violence that avoids feeling mean-spirited at any time, with brutally believable choreography in it's fights and gorgeous artwork to boot. Also, they don't happen too often so that the story leading up to the carnage can be detailed perfectly and more impactful because of it.
 * 6) Plenty of legitimately funny moments scattered throughout that, unlike most manga, don't revolve around slapstick and actually fit each scene quite well. For example, one scene where Musashi shaves Soho's head, but leaves strands of hair that make a goofy face, which Jotaro laughs at.
 * 7) The series also doesn't revolve around fanservice of really any kind, having much more realistic male and female anatomy and relationships, not to mention that each female character is strong and capable in their own right without involving sex. There's also few sex scenes in general, and the one's present are quick and actually have to do with the story.
 * 8) The series brings plenty of questions about the difference between true dedication and foolish loyalty, showing that one's loyalties should not be decided with fear or blindness, and such a thing is worthless in the grand scheme of things.
 * 9) An impressively realistic depiction of the end of the Sengoku Period and beginning of the Takugawa Shogunate, with events that happened around that time depicted almost beat for beat and impressive worldbuilding because of it. It really makes you feel like you're in that era, with plenty of influence on even the art style, and you can really feel the japanese culture of that time throughout.

The Only Bad Quality

 * 1) The aforementioned hiatus, which has left the series as of yet unfinished.