- Critical Research Failure:
- In "Hitler on the Half-Shell", we see Henry's flashback to 1812, where he learned his father was involved with the slave trade. However, it had been abolished in 1807, and there's no indication this is illegal trading. This error is repeated in "Dead Men Tell Long Tales".
- This builds on the error in the pilot episode, in which Henry is shown on a ship carrying a black man described as "property" some time after 1814 (Henry narrates his first death as "almost two centuries ago" speaking from 2014). To add insult to injury, the ship is flying an out of date British merchant ensign - the ensign clearly lacks the cross of St Patrick, which was added to the flag in 1801 after the Act of Union with Ireland.
- In "The Man in the Killer Suit" the fake aristocrat claims that he's not a Lord, he's a Viscount. Despite the fact that a Viscount is by definition a Lord. His fake passport also, incorrectly, contains the title "Viscount". Given the amount of research the woman training him did to help him with his role, you'd have thought she'd spend five minutes checking Debrett's, which would have prevented these errors. Then again, they were trying to fool Americans, who are not known for their detailed understanding of the British aristocracy, as the episode does acknowledge, so this could just be Truth in Television.
- Genius Bonus: In "The Frustrating Thing About Psychopaths," material on the Black Dahlia murder is checked out using the alias J. Ellroy, after the author who became obsessed with the case and eventually wrote a fictionalized resolution to it.
- Jerkass Woobie: Adam is revealed to be this, having suffered torturous experiments at the hands of the Nazis in WWII after his immortality was discovered. Henry and Abe acknowledge this, but also point out that it doesn't excuse his behavior or change the fact that he's a sociopathic asshole and murderer.
- Moral Dissonance: From all we hear, the king of Urkesh was a horrible tyrant who completely deserved to be overthrown, but he was nice to Henry, and the guy who hated him enough to murder people handily crosses the MEH by going after complete innocents including a baby, so we're supposed to like him.
- Moral Event Horizon: In "The King of Columbus Circle," if the killer going after the completely innocent Lydia in his quest to eradicate Urkesh's royal bloodline didn't push him over, levelling a gun on Lydia's infant child did.
- Narrowed It Down to the Guy I Recognize:
- When Burn Gorman shows up as Henry Morgan's psychiatrist, viewers are led to believe it might be the start of a recurring comedic role... as it turns out, he's actually Henry's fellow immortal/stalker "Adam."
- Cuba Gooding, Jr. shows up in "Dead Men Tell Long Tales". He subverts it by not playing the murderer, though this was actually spoiled when the announcement of his casting, a month before the episode aired, outright stated that he would be cleared of murder.
- The Woobie: The poor biochemist from "The Fountain Of Youth." All she wanted was to help people, and her serum did work, but her business partner made her cut corners, forcing her to rely on substandard chemicals and human brain tissue rather than the expensive stem cells, turning it into a toxic brain-damaging formula. And when the police start getting too close, her brother—who'd been providing the brain tissue for her from unclaimed bodies at the morgue—kills her partner. By the end of the episode she's so guilt-ridden and distraught that she's ready to jump in front of a train.
YMMV / Forever