If that sounds like a pretty flimsy premise, that's because it is. Mostly it exists so that there's an excuse to use a bunch of famous names from history: Galileo, Newton, Ghandi, and so on. The E-Gene Holders each use some kind of special power appropriate to the associated name: gravity for Newton, long-distance scouting for Galileo, and so on. It's moderately amusing to see how the powers and people line up. There's also a representative of Jack the Ripper, which doesn't quite fit in with all the benevolent famous figures.
The story starts off following Sio as she gets used to the idea of being an E-Gene soldier. Later on it moves into the history of how the E-Genes came to be, going back hundreds of years. Explaining how Jack fits in turns out to the be the big reveal at the end of the 13-episode series. I wasn't exactly on the edge of my seat as the story moved along, but it was enough to hold things together.
Most of Nobunagun is about fighting the EIOs, and it does a decent job. There's plenty of shooting, slicing, dicing, smashing, chopping, etc of alien monsters. There's no real attempt at realism, which is fine for this genre. The point is large amounts of blowing stuff up, preferably with style points, and that is certainly delivered.
For the most part, Nobunagun avoids the worst of the mindless action anime tropes. There's some fan service but it's not constantly in your face, and the sexual innuendo is mostly kept low-key. The fights aren't one long sequence of screams by the various fighters - there's a bit of that, but not all the time. And the show isn't afraid to poke fun at itself at times.
I don't think there's any danger of Nobunagun being mistaken for a great action anime series. But for a few episodes of simple, straightforward action fun, it's a decent choice.
