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.
In the Harsher side: One of the pacients Black Jack attends (named Crossword) in the OVAs is voiced by Chikao Ohtsuka, who is Akio Ohtsuka's father in Real Life. And he dies at the end of the episode.
One chapter had the author of an extremely popular serial novel close to dying just as he's about to write the last chapter of the story. He winds up dying seconds after finishing the last page. Now go to Osamu Tezuka's page and look under 'Famous Last Words'.
Artists who die either during or just after their magnum opus show up a lot. Early in the series, there was Go Gan, a painter suffering from radiation poisoning who asks Black Jack to keep him alive long enough to finish his painting of the event that caused it. Again, look at Tezuka's last words.
And then there's Tenacity. Made all the more heartrending by the fact that Tezuka's Author Avatar is a major character.
Macekre: The dub scripts for the first six OAVs and the movie are sometimes dramatically different from the subtitles. This mostly manifests as an inexplicable rearrangement, alteration or deletion of several key lines, which can sometimes make the dialogue rather clunky. This is particularly evident in the fourth OAV, in which the entire point of the episode is subverted, and in the movie, wherein one character goes from being tragically misguided to downright Satanic, as well as rendering the movie's Green Aesopanvilicious. OAVs 7-10 are mostly exempt from this, fortunately.
OAV 1-6 were an unusual case. The Japanese license-owners, having seen Tezuka properties in the past handled very badly indeed, insisted that Central Park Media release Black Jack exactly as they received the materials from Japan. CPM agreed, but were surprised to find the materials included an already-produced English-language dub, and no original Japanese-language track. The Japanese license-owners had actually outsourced the dub on their own. It was not until several years later, when CPM licensed OAV 7-10 and the series was released on DVD, that the original JP track was made available in North America.
Tear Jerker: Many, MANY stories are very heartbreaking. Special mentions go to Black Jack's backstory, Pinoco's backstory, the violinist Morozov losing his fingers despite Black Jack's efforts, the whole deal with Nadare the intelligent deer, and the case where a cute cashier with her eyes damaged by a bomb can only be operated to see again for five minutes so she can identify the man who detonated the bomb AND blinded her in the first place...