Nobunagun has a weak middle section that almost blows the credit it earned from the strong second episode, but recovers nicely for the finale.
The Weak Middle
The middle section running from episode 3 Capa’s Island to about episode 7 Musashi Wonder is plagued by a loss of focus, creepy fanservice, and a complete absence of Kaoru.
Given that it was the interaction between Kaoru and Sio that made Evolutionary Invasion Objects into such a great episode, this was as a major mistake in my opinion. I won’t say that these episodes are as bad as the Island episodes in Nadia: Secret of Blue Water, but 5 filler episodes in a 13 episode series is not a good sign.
The Strong Finish
However Nobunagun starts recovering the momentum from episode 8 Tunnel, and builds to a strong finish through Operation Stone Forest Part 1, Part 2, and Nobunagun (11, 12, & 13 respectively).
The fun comes back, Sio gets to be her batshit crazy brilliant best, Kaoru gets screentime again, and then there’s that [SPOILER DELETED] about Jack the Ripper in episodes 12 & 13.
Speaking of which, do NOT visit the Wikipedia page until you’ve seen the episodes in question. TV Tropes at least hides it.
Trust me on this.
The finale isn’t perfect, particularly in terms of the relationships at the end, but overall it is well worth persevering through the weak middle for. Definitely a series to watch once, and it may improve on a second viewing.
EDIT: I just found a decent version of the OP on YouTube, so here it is: