These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Best Known for the Fanservice: Never mind that the series was a critical darling, which gained a cult following and even influenced political movements in the 70s, anyone you talk to today who took it out of the school library is likely to remember all the sex and nudity.
Complete Monster: The lord of the Hioki Domain in the first series: among many other misdeeds, he rapes a peasant girl who is serving at his residence, then after she's drowned herself in despair, he spitefully hacks up her corpse and sends it back to her village, bundled togther with rotting animal meat.
Growing the Beard: Kamui Den was a key milestone in manga, as a medium, growing the beard—so much so, in fact, that the "God of Manga" himself, Tezuka Osamu, would praise it for bringing "Serious drama, characterization, and ideolgy to manga." Tezuka acknowledged a substantial (if grudging) debt to the Gekiga movement, whose influence on his later, more adult-oriented work is clear.
Harsher in Hindsight: The injustices of Edo Period Japan, often regarded as a period of stability and peace, are treated with unflinching honesty in Kamui-den. Disturbingly, some of the class-based discrimination depicted in the series persists to this day, though no longer in institutionalized form.
Ho Yay: There are significant gay and lesbian overtones in the early volumes of the second series.
Sequelitis: Very much a YMMV thing. The 80s reboot of Kamui Gaiden (itself a sequel/spinoff of Kamui Den) is by no means bad. But it lacks much of the subversive punch that made the original series a classic. Sadly, this is still the only portion of the Kamui franchise ever to have been published in English.
Values Dissonance: Western readers will (or rather would) likey experience this, though it's hard to say whether the often brutal treatment of female characters is more due to the author's nihilistic bent or actual historical attitudes toward women in feudal Japan.