@Zeorn:
Comparing manga and novels are a bit of a stretch. Vagabond is a work of art, it is just beautiful to look at no matter if you are interested in the story or not. Even if the story wasn't good the artwork can more than make up for it, draw in readers and keep them. For novels all they have are the narrative, characters, and world building which requires you to imagine it.
I think you're downplaying the importance of aesthetics in novels a little bit. Writing requires all sorts of craftsmanship that can be beautiful and awe-inspiring too. It's not only the merit of the story itself that matters.
Anyway, the same story can be considered great or mediocre depending on who is telling it, even more so in such different art forms such as novels and manga. Vagabond can be great while Musashi is mediocre, and vice versa. I'm just asking the perspective of people who have read both.
I'm well aware that Inoue is a pretty good mangaka, but in a world where we can basically read anything whenever we want, Vagabond was never a priority to me because of my lackluster experience with Musashi. And not because Musashi was poorly written (it was good as far as I remember), but to me it felt like the story was too lengthy without ever finding a meaningful closure for Musashi's growth and love story.
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@HeartOfDarkness:
That's the basic concept of Vagabond, yes.
But ultimately Inoue, somewhere along the line, goes off into his own direction and starts to use the entire premise and the characters to convey incredibly personal and philosophical themes.
Even the main character starts off the series with no ouch of regard for human life and just being a "beast" all around but then he starts to transform, alongside the series, and becomes more of an wise and incredible person.
Oh, the books are not only ass kicking. Very far from it. It focuses much more on Musashi's growth as a person as the primary virtue of a samurai.