Very popular in Italy and France. Ikeda even got the Legion d'Honneur for her work, the highest possible honor a foreigner could receive in France and other honors from Italian otaku fans and Italy's government.. In Italy, the series is practically in the same league with Sailor Moon, Dragon Ball, Saint Seiya, and Fist of the North Star in fame and its popularity is such that it still receives re-runs on local channels in the country (something that the above aforementioned anime did not receive for a while until recent remakes and sequel OVAs and series with the exception of Hokuto No Ken).
When Fersen meets Oscar, he thinks at first she is a man. Rosalie is also flat-out in love with Oscar for a good portion of the series and apparently retains some feelings for her into the Distant Finale after having married Bernard.
On the other hand, Oscar gets pretty mad about it when Jeanne publicly accuses her of being a lesbian. (Her reaction in the manga is even stronger than in the anime.) Of course, given the historical setting, she likely wouldn't want such a reputation, even if it was true.
In chapter 4 three ladies at the ball fangirl over Oscar who they clearly know is a woman. They call her dashing, wish that she would come over and talk to them, and then all subtlety is lost when one says that she wishes Oscar were a boy so that they could get married.
Jeanne having Nicolas whip Rosalie to force her out of the noble mansion she was living in... then manipulating him into killing the kind woman who took her in AND burning down her house so she could become the heir.
Saint-Just the Nobility Serial Killer planned to kill a Duke and his wife and child brutally, just to send a message.
Henri de Guemene killing a street urchin merely for robbing him. Specially despite Rosalie's desperate tries to get him to spare the victim.
Polignac (in the anime), when she subjects the mentally fragile Rosalie to psychological abuse, deception and eventually blackmail in order to force her to leave Oscar and join her family. Made doubly worse by the later revelation that she intends to marry her off to a very creepy man whose attentions caused her other daughter to commit suicide. Also, she gloats sadistically once Rosalie is broken and caves in to her demands:
Polignac:"Now, Rosalie, call me 'Mother'!" [Evil Laugh]
Narm Charm: Oh boy, is the anime full of it. From the Pastel-Chalked Freeze Frame to the melodramatic Call My Name, this show was the trope setter for a lot of the devices you find in "girls" anime today. The fact that it's a late 70's show speaks for itself.
One-Scene Wonder: Napoleon Bonaparte has only one speaking appearance and a non-speaking.
Values Dissonance: Guiche's attitude towards Charlotte and Polignac's obsession with marrying her off despite her being just 12 years old are partially explained by how it was normal, back then, to have high-class girls getting married as soon as they were out of puberty, if not even earlier. Antoinette was indeed lucky to have a fiancé and husband not much older than she was — at least, well, before things went From Bad to Worse.
The instant assumption that a prostitute must be a terrible person also raises a few eyebrows these days.
What an Idiot: In the manga, Hebért accuses Marie of incest with her surviving son. After Marie Antoinette's reply, Hebért finds himself surrounded by women and mothers who feels offended by his words, and Robespierre starts searching for a reason to get him executed (he'll get it).
Also, cardinal Louis René Édouard de Rohan, Bishop of Strasbourg. With his family having prince étranger status [a status above most nobles and below only the House of Capet (including the Royal Family, cadet brances of the House of Capet and legitimitised natural children (and their male descendants) of kings], in the House of Rohan case due descending from the Dukes of Brittany (former monarchy) and hereditary control of the Archbishopric of Strasbourg (an ecclesiastical principality formally part of the Holy Roman Empire, even if part of its territory and its seat were under French control)) and his older brother being the Prince of Guéméné and in the queen's good graces, he had no excuse whatsoever to not know that royalty only sign with their given names. He gets a particularly hard Lampshade Hanging, as it's Louis XVI, theNice Guy of the series, to point out he should have known (that and the calligraphy was different from Marie Antoinette's, but Rohan had never seen her handwriting).
The Woobie: Some of the characters, like Oscar and Andre have their moments. Rosalie takes the cake, though: her foster mother dies, her sister turns out to be a huge bitch, not to mention her sister's actions started the chain of the whole events and so on... God, the girl seriously needs a hug.