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.
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.
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.
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◊ (episode 11 is slightly different, however, with Kancolle version of Akashi and Ooyodo◊ being paired up with Shizuka and Iori instead due to the fact that Arpeggio doesn't have Akashi and Ooyodo yet). Haruna and Kongou's artwork are done by Konishi, who contributes a lot of art to KanColle; this explains the wider eyes in the said art, in comparison to the original Arpeggio designs, especially Kongou's. 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.
Someone actually made an AMV using Ars Nova's opening with Kantai Collection images. It fits so well, until fans wanted nano to sing the opening of the upcoming Kantai Collection anime.
Fan-Preferred Couple: While the anime tries to make some girls compatible with Gunzou (Iona and Takao), some fans would rather pair those and other girls with each other.
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 completely 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 undergoing extensive modernization prior to World War 2 and being reclassed as fast battleships.
The music video for Savior of Song is this too, since you have to look up the ship's hull number (DDG-174) to know that it's Guided Missile Destroyer Kirishima they're singing on.
Les Yay: Haruna is collecting a harem of her own. As well as Hyuuga for her Onee-sama Iona.
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 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.
Shipping: As mentioned before in the Fan-Preferred Couple trope, and no pun intended. This includes Haruna/Makie, Takao/Hyuuga, Iona/Hyuuga, and Maya/Kongou. Pretty much like, again, Kantai Collection.
Enjoyably played with when Gunzou and Hyuuga go on a mission by themselves for over a dozen chapters. Among other things, it includes Gunzou telling Hyuuga his backstory and emotional motivation, Gunzou and Hyuuga telling each other "I can't lose you", and ends with Hyuuga desperately begging Yamato and Yukikaze for a little more time to save Gunzou, despite being already reduced to her core and the near-certainty of being captured by Ise.
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.