Adaptation Displacement: While most of the Tezuka characters who show up here did make earlier stateside debuts in one form or another (even if only as extras in other Astroboy productions), for a time this was what all of them (with the possible exception of Black Jack, whose OAV series enjoyed modest success in the West during the late 90s/early 00s anime boom) were best known for in the English-speaking world, though Vertical Inc.'s recent blitz of high quality Tezuka manga translations has done a lot to change that.
Fridge Brilliance: The Final Boss music is titled "World's Strongest Robot". This both refers to Pluto, as he's the leader of the "World's Strongest Robots"; and Garon, who the Character List refers to as "the most powerful super robot sent to Earth".
That One Boss: Atlas, when fighting him with Dr. Black Jack at the bottom of the map, who can't be touched at all. A single hit from Atlas's stray beam attack, and you lose.
Actually, it's three. At least in easy mode. And if you stay at the top section of the map while the beam is at the bottom, as long as Dr. Black Jack is out of view, you're okay.
In the NA normal difficulty he can survive at least one hit.
The Jousting Duel with Blue Knight, which requires landing a few hits while being a One-Hit-Point Wonder regardless of your life level. Part of this is due to being a Guide Dang It, and another part is due to having to replay a lot of the level if you die.
The Untwist: Blue Knight being President Rag. The gratuitous flashback makes it screamingly obvious.