Osamu Tezuka has an incredibly diverse body of work. There are his high-profile children’s works like Kimba the White Lion, Astro Boy, and Princess Knight. While they don’t talk down to their audience they are clearly for children. You then have his strictly seinen works like MW, Adolf, and Swallowing the Earth. They are clearly for an adult audience with mature themes. But Black Jack sits firmly in the middle of these two extremes. It ran in a shonen magazine but it reads more like a seinen title. It has a fine balance between that make in an extremely accessible but weighty classic.
Black Jack is not just a genius surgeon. He is the quintessence of a genius surgeon. When you have a medical issue that no one else can handle you go to Black Jack. There are only two catches. He is an unlicensed surgeon and therefore his services exist outside the law. The other is that he is astronomically expensive. He charges millions of dollars for his services. While he is not a complete bastard, as he often waves his fee for people honestly in need, he hardly advertises that fact. The manga is mostly episodic tales of Black Jack’s strange cases with everything from operating on terrorists in the sewers to dealing with ectoplasmic patients.