Americans Hate Tingle: Non-Japanese viewers are divided over the series. Some feel that the series (and the author himself) would try to glorify the Imperial Japanese Army, especially given what Tokyo is trying to do with the constitution under the Abe government. Others feel that it shouldn't be the case since it delves into the work of covert operations set prior to the beginning of World War II. This so far has made a few viewers drop the series.
The series is very popular in Japan considering that it got second place on Tokyo Anime Awards' Animation of the Year Fan Award (behind Yuri!!! on Ice), won the Nogizaka46 Award (Monthly Newtype Joint Special Award), was ranked #6 in NHK's Best 100 Ranking Poll and #5 in the female voter's poll. Many non-Japanese viewers were surprised with the series' popularity which made them wonder if this had to do with the Cast Full of Pretty Boys.
Anime/Manga:
Adaptation Displacement: Most who were able to watch the anime/read the manga wouldn't know that it started as a novel series.
Better on DVD: Despite being an episodic show, one can get a lot more enjoyment watching the episodes back to back than waiting a week in between. It's a lot easier to keep track of who's who and remember faces. Not to mention the ability to watch them in chronological order is a huge bonus.
Broken Base: "Miscalculation"'s reveal that the series is going to be an episodic show and that Lt. Sakuma was a Decoy Protagonist threw a lot of viewers for a loop and led to much arguing over whether an episodic direction would be good or bad for the show.
Epileptic Trees: After "Code Name: Cerberus" aired, many viewers joked that Amari would bring Emma back to Tokyo and raise her as the agency's lone female spy with the rest of the agency. The show's own character designer even got in on this and posted some drawings of such on his Twitter.
Hilarious in Hindsight: Tessho Genda plays Col. Muto of the IJA's General Headquarters, who really doesn't like D Agency by way of Interservice Rivalry. He previously voiced Sam Fisher in the Splinter Cell games, a spy who has a hard time getting cooperation from law enforcement and intelligence agencies for the same reasons. Only this time, he's on the receiving end.
Narm: Oikawa’s over-the-top confession in "City of Temptation" can make one viewer rolled their eyes on how ridiculous it is.
No Such Thing as Bad Publicity: Some have seen this series because of Beatrice the Golden Witch talking about it in her "How to tell a Bad Anime in One Episode", though she notes that it isn't a terrible series so much as one that flaws that made it so she couldn't watch it, those being lack of characterization, and the ham fisted morals. The viewers courageous enough to see if they would enjoy it find that it isn't terrible, though she never called it that. It helps that she said that some people might enjoy it regardless of those flaws.
"Double Joker Part 1" presented another spy agency known as Wind Agency sponsored by the Imperial Japanese Army which would act as a Foil to D Agency and viewers expected a huge showdown between them similar to Light and L. Then, it turns out that in "Double Joker Part 2", the Wind Agency are nothing but a pathetic bunch of spy wannabes that got utterly owned in a few minutes by Col. Yuuki who gave Col. Akimasa a "The Reason You Suck" Speech and it all ended with Col. Akimasa committing suicide.
Same thing with Miyoshi: appearing to be either the most competent, or at least the most special, of the spies in the first couple episodes opposite Sakuma, he doesn't even get to speak in his focal episode "Coffin," in which he has died before the episode has even begun. He gets more lines in Odagiri's episode, "Double-Cross."
In both "Asia Express" and "Codename: Cerberus", the D Agency spies of each episode strike up conversation with children and even play with them out of the blue. Especially in the latter, he even picks up a toddler girl and walks around with her to show her some dolphins. In the 21st century, strangers interacting with children would be much more likely deemed to be far, far more sinister, and their parents would be much less likely to let their children play with them.
The school director expelled Akira for using Combat Pragmatism against his opponent. This sort of reasoning is unbelievable in modern standards considering that Akira was just defending himself and had never used his pocket knife. And yet, the director seemed fine about students fighting each other and bringing pocket knives in school which is no longer applicable today due to various incidents of schoolstabbings and killings committed by minors which is a huge social issue in Japan.
on Tokyo Anime Awards' Animation of the Year Fan Award (behind Yuri!!! on Ice), won