These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Broken Base: The CGI adaptation has been mostly positively-received by viewers not really familiar with the source material (and indeed, the pre-order figures, while not Girls und Panzer-levels, predict that it will make a modest profit). For the small circle of people who've followed the manga from the beginning however (one has to be reminded that this was a very niche series that catered to fans of wartime IJN ships), the anime is just one long string of bad compromises for the sake of fitting the story into a twelve episode runtime.
One would imagine if the series gets a stinger at the end of the season featuring all of the stuff taken out (which would make people wonder why they were excised in the first place), the latter group would go ballistic.
Episode 10 is sure to be one hell of a base-breaker, since Takao died. Well, irrestorable until they got another supply of nanomaterials, but it is treated like death nonetheless. This is somewhat ameliorated by the fact that Takao makes an appearance in the subsequent episode as a hologram.
The fanbase for Kongou and Maya.
The Sleeper Hit status of Ars Nova sales-wise, and the vocal interest of the director to do more of the series, despite how it discarded most of the possible plot threads that could be used as sequel hooks, has caused the grumbling to continue for manga readers, while those exposed to only the anime are ecstatic at the possibility of a sequel.
Critical Research Failure: Not on the part of the production, but on the part of the translators for the CR English stream. Likely to go unnoticed for people not familiar with the actual Imperial Japanese Navy ships featured, but for those watchers who are, the experience is jarring. See how Nagara was called a battleship (she isn't; Nagara is a light cruiser), or Hyuuga being called a "fast battleship" (the historical ship wasn't) despite the actual term used in-series being dai senkan, literally great battleship or dreadnought.
The fans are not exempt either, sadly enough. A number of them believe that Hyuuga is mislabeled as a Battleship in the translations, "as opposed to a battleship/carrier hybrid which she was her whole life." However, once you do a bit of research into the historical Hyuuga, one finds not only was Hyuuga converted into a hybrid in 1943 (as a response to the losses of Japan's career fleets at Midway), but she started life in the 1910s as... A battleship.
Crossover Ship/Intercontinuity Crossover: With Kantai Collection. Paired artworks of same-named ship girls of both sides appear as end-of-episode panels on every odd-numbered episode of Ars Nova, with the exception of episode 1. Episode 3 has Haruna, episode 5 has Kongou, episode 7 has Takao, and episode 9 has Maya◊. Haruna and Kongou's artwork are done by Konishi, who contributes a lot of art to KanColle. Then there's the entire December 2013 collaboration event, where Iona, Takao, and Haruna are controllable allied units...
Additionally, in Episode 7 of the anime, when Takao is having her imagine spot of being the Blue Fleet's flagship, she imagines Gunzou in an IJN Admiral's uniform (as opposed to his Captain's uniform in the manga). The player character of KanColle is an IJN Admiral.
Ensemble Darkhorse: Takao by far seems to be the most popular Mental Model, if not the most popular character in general, among fans.
Genius Bonus: I-400's Chinese dress is a reference to the actual sub's cargo runs between Japan and occupied Chinese east coast.
Kongo's general feel of Britishness (Stiff Upper Lip, Lady of War, having tea and cucumber sandwiches in the English style) becomes more understandable when one learns the IRL Kongo was designed and built in Britain.note Kongo was the last Japanese capital ship to be built outside Japan; her sisters Hiei, Haruna and Kirishima were laid down in Japanese shipyards. All four were originally classed as battlecruisers, before being rebuilt and rearmored prior to World War 2, and reclassed as fast battleships.
Like You Would Really Do It: When Japanese special forces raid the Iwo Jima base and kill most of the 401 crew, it's pretty obvious that it's all part of some plan.
And then there's the "death" of Gunzou in episode 10. They milk it for all it's worth before the last minute save comes in.
Memetic Sex Goddess: It's common for fans to declare Takao the "Tsundere Heavy Cruiser, flagship of [their] hearts," inspired by Maya's declaration of the same to Haruna and Kirishima.
Memetic Mutation: CARNIVAL DA YO! after Maya's Broken Record ranting. Carried over to Kantai Collection, where in the December 2013 collaboration event, Maya's an encounterable boss, and players have learned to hate it whenever she spouts the line repeatedly while beating on their fleets.
The Woobie: Iona really gives off this vibe in episodes 9 through 11, as her attempts at friendship with Kongo are rebuffed, I-400 and I-402 show up to sink her, and she's eventually forced to kill her sisters.