I thought the octopus was cute! Which I think was the only thing I liked about it. It got hyped when it came out as this great fantasy-historical m/m, which was on thinner ground at the time, but I couldn't handle how much of a pill Grace was about everything, and the Evil Irish Terrorists! plot didn't work for me either. Plus the whole time travel thing felt really handwavy? I know it's hard to stick a time travel plot, but this left me going "...I GUESS?" at the end. And the romance didn't especially work for me either.

tl;dr: I liked this book better before I actually read it.

ETA: My review at the time:

Part of it was that it was pretty awful at female characters, as in there was one, and she spent her whole time disliking other women because she was masculine and therefore smarter than them, and then acting like an idiot about everything. I think it passed Bachdel only because she mocked some suffragettes.

Part of it might be that it felt too constructed for its own good. Because of the nature of the title character, there had to be a lot of careful balancing of moving parts, but honestly the end felt less like a Xanatos Gambit and more like a Xanatos pile up, with the author just flinging plans at the wall for no reason, and then setting the resulting chaos to the music of Arthur Sullivan. Maybe I'm not smart enough to read this book, but I didn't get what was going on, and I didn't care.

Mostly I guess the characters were jerks; I didn't care what happened to them, and the romance was underplayed to the point where instead of making me root for the characters, I just made me more tired of them.