i had read a lot of manga based on edo japan, or with characters hailing from that time period (time travel, etc) but this is the first manga that try to portray the life there as accurately as possible, not just for the cool factor. thus history buff like me might find this enjoyable, and i especially find the yakuza code interesting.
however the two main characters are not very interesting. they are superhuman god-mod characters that can kill an entire town just by themselves. they have very nice physique for former slaves with little to no food. but that might not be too bad of a point since the characters are just vehicles to showcase the lives of Japanese people in edo period, and also to deliver a line here and there about freedom.
arts are great, but less manga and more comic.some people might not like that, but i think it carries the tone of the story well. i personally think this manga is more shounen than seinen, bloods withstanding, due to the very shounen-like characters, black-and-white morality, and simplistic plot. that does not make this bad - it just mean some people might get disappointed.
all in all, a good manga. it is short too, so just try it!