The premise of the series is Captain Drake Morass is a conman/pirate/charming ass who has started to think about his retirement. Having alienated the Empress of the Dragon Empire (China) and lost his meal ticket there, he's decided he will settle on nothing less than rulership of his own kingdom. Rather than attempt to take over an existing kingdom, he will form his own by uniting the buccaneers of the Pirate Isles.
Unfortunately, this plan has the small issue everyone in the Pirate Isles knows Drake Morass is completely untrustworthy. So, he's recruited Captain Keelin Stillwater who is known for his honor and Elaina Black for her status as the island's closest thing to royalty. Both of them are better qualified to lead a hypothetical kingdom than Drake himself. While the first book dealt with his establishing of the kingdom, the second deals with him cementing its existence and that requires defeating a massive navy coming to kill them all. There's also looting ancient treasures, political intrigue, and even a romance.
My favorite characters in the book are easily Keelin and Elaina for much the same reasons they are better leads than Drake. Keelin wants to be a gentleman pirate but such a thing doesn't really exist in this world and it's led him to an ill-fated romance with a "good" woman who is unsuited for the life of a pirate's wife (mostly because she wants to be a pirate herself). Elaina channels everything I loved about Asha Greyjoy while moving her to a more Caribbean-esque environment.
I actually found Keelin and Elaina's relationship to one of the more endearing parts of the novel with it interesting how the former has thrown away a strong connection with the latter out of "respectability" while coming to regret his choice. The fact his new girlfriend, Aime, doesn't really want anything to do with him save how it benefits her position as a sailor, was also a nicely unsympathetic take on what would normally be a common romance story. The "good girl" winning over the "bad girl" with the power of her protagonist-ism. Here, Aime's growth as a sailor and character takes her further from Keelin than closer.
The Fifth Empire of Man is full of action, exciting naval battles, and twists which I honestly didn't see coming. It's cool to see the master manipulator characters aren't omniscient either. Drake Morass plays his cards a little too close to his chest and when things go array, has difficulty getting things back under control before they spiral completely out of his hands. I also liked Drake's relationship with Arbiter Beck as it is an anti-romance. Neither of them particularly like the other but are willing to play at being lovers because it's temporarily convenient.
In conclusion, this is a really good novel and serves as an excellent end to the duology. Characters triumph, die, fail miserably, or are avenged. I think Rob J. Hayes could have extended this to being a full trilogy but I'm happy with what I got. I think this series is easily be one of the best offerings of 2017 and stands up there with Joe Abercombie and Mark Lawrence.