For a manga all about sentient battleships personified as cute girls, Arpeggio of Blue Steel is really, really good.
It's really rare to find manga about naval battles, and it's even rarer to see it done in this way, with a plot that makes you think "contrived!" but actually turn out to be well-thought out and reasonable. I'm really surprised at how the mangaka manages to turn a seemingly strange premise into something as serious and intriguing as this one.
The only criticism I have for this manga though is that while the battleships are growing and developing (I'm frankly amazed by how much they have developed and how central it is to the plot), the humans have... well... not. That's not to say the humans are poor characters, by any means, but it doesn't feel like any of them, Gunzou in particular, are changing at all.
Now that isn't precisely a complete downside, as this isn't one of those fast-paced mangas where the main character does a bazillion things within forty chapters, and Gunzou is also an adult, so it's understandable why he wouldn't be as susceptible to change as, say, the battleships who have just recently become sentient in comparison. However, I would definitely like to see more backstory on Gunzou and slightly more focus on the human crew on Iona. It would certainly give more perspective on why exactly they're so intent on their goal, that's for sure.