For the first time in the series we see clearly what's been hinted at all along--that this alternate history is not just our history performed in slightly different costumes. The dragons are not just window-dressing; having the most powerful weapon of the 19th century be non-technological and thus equally available to both pre- and post-industrial societies makes a very real difference in the history of colonization. Watching the consequences of that play out left me with a deep sense of satisfaction at seeing something done right.
Part of me finds the cliffhanger ending exasperating. But. . .just like the world building, the character development is inevitable. From the moment the Admiralty makes its pronouncement, we know what Laurence's response, and the resulting consequences, have to be. That's what made reading the last fifty pages so wrenching; knowing exactly what was going to happen, and yet not being able to stop it. Ending the book anywhere in there wouldn't have been an improvement; to avoid a cliffhanger, it would have had to have stopped immediately upon Laurence's return to England. And in that case, the book becomes a travelogue, not a novel, because it's only in those pages that we really get to see Laurence taking action, rather than just allowing the world to act on him.
As much as I love the world building, I think it really needed that paralellism, the clear extrapolation of unavoidable consequences in both setting and character, to be as strong a book as it is.