Strong voices and good character interactions make for wonderfully engaging slices of life at the Naval District. The girls' friendships are heartwarming, their hijinks are hilarious, and their losses and near-losses are tearjerking.
Unfortunately, the campaign against the Abyssals doesn't keep up its end of the bargain. The naval combat itself is nothing special (mostly the ships kind of sail around and take shots at each other...Girls und Panzer and High School Fleet had better attention to group tactics and naval combat, respectively), and the larger campaign has a ham-fisted WWII allegory that falls a little flat. I could forgive the sneak attack on the naval district (that's not exactly how the Pacific War started, but it's in-character for the Abyssals), and Akagi's dreams of WWII repeating itself could have been the seed of an interesting plot, but when the Battle of Midway Redux is looking like a repeat of the original, the admiral just pulls a few instant repair buckets out of his hat and swoops in with Zuikaku, Shoukaku, and Yamato to save the day.
Related to the shortcomings of the naval campaign is that we don't really see why it matters. We are told in the opening of the first episode that the Abyssals have driven humanity back from the sea, but we never see any of those humans, or indeed anything of the world beyond the Naval District and Japanese fleet. Contrast this with Arpeggio of Blue Steel -Ars Nova-, which had the same twelve-episode limitation, but showed the politics of the world and other efforts trying to deal with the Fleet of Fog (while also finding time for slice of life and a naval campaign), and also made the Fleet of Fog into interesting, engaging characters in their own right (while the Abyssals, as depicted, are little more than Generic Doomsday Villains...and even then, they're pretty light on the 'doomsday').
I hear that the movie has better animation for the naval combat and digs deeper into the origins and activities of the Abyssals, so we'll see how that goes and what happens with season 2. Until then, I've got a couple fanfic recommendations that I think do a better job with the "moe anthropomorphized WWII warships" world than the anime (I'll put up a proper fanfic recs page, with more details and a few more recs, but I got inspired to write this review first):
- Belated Battleship, for the 'epic campaign' flavor. (May contain more Eagle Land than some folks want, but it focuses on all the navies.)
- Things Involving Shipgirls That Are No Longer Allowed, for pure slice of life.