[Might contain a few small spoilers.]
Well, I stayed up until 4 am finishing the book, slept for a few hours in which I dreamt about it, then woke up and tossed and turned thinking about the story until it aggravated me enough I had to write about it. I just don't know where to start because there's so many elements of this book I want to get down.
First of all, fans of the Gentleman Bastards, don't go into this book thinking it's going to be like the first two. Upon reading the summary, however long ago it was, I sort of expected the usual entertaining, highly anticipated, complicated trickery of Locke Lamora and Jean Tannen from the previous books, only this time with the added benefit of a rival--the mysterious Sabetha, once devoted member of the Gentleman(woman) Bastards now forced to work against her previous friends and lover. Sounds pretty exciting. Instead it turns out to be a few infantile pranks between the two, which they laugh about together over dinner. That's the extent of the rivalry.
It's less The Lies of Locke Lamora and more a romance, centering around Locke attempting to woo Sabetha in childhood through the interludes and present day through the main storyline. Both of which could be frustrating because Locke is reduced to a simpering, lovesick puppy during most of it, while Sabetha...Oh boy, how to explain Sabetha? She's the fiery, short tempered redheaded trope. Locke constantly has to walk on eggshells around her, and so it leaves to question why he likes her at all. Her character falls flat compared to the other female characters we've seen, which is a shame.
To be honest, I'm not entirely sure who or what the antagonist is supposed to be. You have the Bondsmagi, but there's not anything particularly threatening about them. From the very beginning Locke and Jean are even told no harm is going to come to them and after the elections they'll be free to go and do whatever they please. The Republic of Thieves sounded wicked and awesome, but it's not actually a republic of thieves at all. It's the name of a play Locke and the other Bastards performed as teenagers. You might even be thinking the play has some kind of significance, foreshadowing or some such, but it doesn't. I'm unaware what relevance The Republic of Thieves the play has to do with the story (except maybe how the book is all about Locke trying to bang Sabetha, and during the production of The Republic of Thieves is when he first gets to bang her).
Poor Jean is labeled as the brute sidekick with no relevance of his own to the story except to push Locke and Sabetha together. In Red Seas Under Red Skies you begin to see Jean as a unique character with his own story to tell, but in The Republic of Thieves that backpedals and he's entirely overshadowed by the Locke/Sabetha relationship.
I know my 3 stars might seem strange in light of the negativity in this review, but it's not that I hated the book. I was simply (heavily) disappointed. The Locke and Jean wit is still present. The story itself is not bad, nor are the characters or the writing. I expected one thing and got another, through no fault of the author's. I still look forward to the next installment (especially because of a plot twist regarding Locke's past and identity), but will be desperately hoping Sabetha stays far away.