Vagabond is a graphic novel written and drawn by by Inoue Takehiko. It depicts the story of Miyamoto Musashi, and is an adaptation of the novel Musashi by Yoshikawa Eiji. In its English version, it is being published by Viz Comics.
Graphically, I'd put this manga above average, although the art actually ranges from excellent to mediocre. The fact remains that the guy can certainly draw: very good anatomy, great physiognomy, and excellent crosshatching. Where it usually falls apart is in the more manga-esque scenes, which appear really out of place in this comic book adaptation of the kensei's life.
Story-wise, I find it so-so. For most people, it's probably very interesting, but I own the Samurai Trilogy, a movie trilogy that is based on the same novel, and up to now there haven't been any difference between the movies and the manga.
Vagabond has been compared to Blade Of The Immortal, and while it is true that they have the same audience, the latter is much better, both artwise and storywise. IMHO, of course.