I just finished watching this series and true, there were a few gaps in the plot as well as some of the character's stories weren't explained enough in detail. Instead, the plot changed focus on Sannova, which left all the other stories such as Nakiami's sister arc not so important as to Lady Sannova changing the world.
Well, I guess im a bit lazy to say anything else and I would agree that the characters have developed well throughout the series but some were a bit disappointing and not so interesting for me in the end such as Yango. As for Akiyuki, Nakiami and Haru, they developed fine throughout the series.
well all in all 8.5/10. Ending could have been better and some characters did need more character development and explaining throughout the series. Still liked it though