- Bizarro Episode: Once Upon a Time Space, which is a pure fiction with an actual plot.
- Cult Classic: Once Upon a Time... Life. Which has managed to remain a reference for French people even after it ended (to the point there was a DVD re-release 30 years after it began airing, and it is re-rerun regularly on kid's channel Gulli).
- Ear Worm: Johann Sebastian Bach's Toccata and Fugue in D minor in Once upon a time... Man.
- Fridge Logic: The conquest of Gaul is told solely from a Roman perspective, and this part of the history of France is barely touched upon. This may have to do with a fear of plagiarism, as the combination of a strong dimwitted redhead and a smaller, somewhat smarter guy was a main theme of the series - and French popular culture had already a familiarity with the Gaulish version of those two. The fact that a "gaulish" version of Maestro would have been an almost complete copy of Panoramix, and that Roger Carel, Pierre's voice actor in French, is best known for being the voice of Asterix in the animated feature films, would have made things even more hilarious.
- "Funny Aneurysm" Moment: Towards the end of the eleventh episode of Man, the roof of the cathedral Maestro is working on caves in. This was meant to be a Funny Moment, but on April 15, 2019, a fire broke out in Notre-Dame de Paris, causing the roof to cave in and making this scene harder to stomach.
- Germans Love David Hasselhoff: The first series is very, very well-loved in Spain and in Spanish-speaking Latin-American countries.
- One can also find DVD sets in just about any Israeli bookstore.
- The third series is HUGE in Italy, where the series is not only reaired very often, but also the DVD's (which came with books explaining in a more elaborate way the facts exposed within each episode) are reprinted every 3-4 years.
- Hilarious in Hindsight: The third episode of Man casually mentions that Neanderthals and Cro-Magnons lived side-by-side for 5000 years. It is now understood that modern Europeans are descendants of both Neanderthals and Cro-Magnons.
- Magnificent Bastard: Episode 8's conclusion about Muhammad's legacy:"Its been said that a man is brilliant if he can start with nothing, dream of greatness, and achieve his dreams. If that statement is true, then Muhammad was a genius."
- Narm: In an attempt to minimize the Nightmare Fuel below, the Spanish dub (plus the Latin-American one) used a far peppier and very catchy opening song performed by child singers. The combo of the cheery music and the creepy images is... really, really weird.
- In the Latin-American dub, Viking!Pierre's death is very sad. Pierrette's scream as he dies, however, is so ridiculous it almost ruins the scene.
- Nightmare Fuel: The opening of Once Upon a Time... Man. The last sequence has a terrified Pierre running toward a space launch while being chased by hostile men. Then, the rocket take off and the Earth blows up. The ominous organ music doesn't help. Very educational kids! Happy nightmares!
- Retroactive Recognition: Sharp-eared Latin-American Spanish fans will recognize the VA's for Pierre (Salvador Nájar), Le Gros and Le Nabot (Álvaro Tarcicio) and Pierrot (Eduardo Tejedo) as the first Luke Skywalker, the original Captain Glovall and the classic Genzo Wakabayashi, respectively. Also, Le Teigneux is voiced by Narciso Busquets who voiced Professor Ratigan in Disney's The Great Mouse Detective.
- Suspiciously Similar Song: One of the main themes, such as plays when Alexander the Great is fighting the Persians in Episode 5, sounds like Khachaturian's Saber Dance.
- Not to mention the jaunty theme that plays at the beginning of Episode 14 sounds an awful lot like a counterpoint to Funiculi Funicula.
- They Wasted a Perfectly Good Plot: Episode 3 of Man only offhandedly mentions that Neanderthals and Cro-Magnons lived together in Europe for 5000 years. Episode 2 or 3 could have utilized the premise and shown how the two said peoples might have gotten along.
- Similarly, later episodes mention, but don't show the Protestant Reformation.
- Values Dissonance: In the Once Upon a Time...The Earth episode, the portrayals of native Africans look incredibly racist even for something made in the 1970's.
YMMV / Il était une fois...