A solid entry in the series, but starting to strain the suspension of disbelief that the same six-seven people are constantly at the center of these epochal, shattering moments for humanity. So, on that note, I'm glad that they're moving into the "final" trilogy of The Expanse with the following book, Persepolis Rising. As for THIS book, it brings a generally satisfactory conclusion to the story of Marcos Inaros and his Free Navy's rebellion against Earth/Mars/OPA. I'm basically just glad to see Marcos go away (spoiler, but c'mon, you knew it was coming) because he's a paper-thin caricature of an evil bad guy who was never really developed much beyond being a necessary plot agent. His background with Naomi was rather insubstantial, his relationship with their child almost Darth Vader-ian in its comical abuse... what he did to Earth is genuinely disturbing, and I almost wish they spent more time dealing with the effects of the attacks, but the background info we get via Avasarala does a pretty good job of conveying just how fucked things are.
That said, the fact that the 1300 new worlds and many new colonies that we know are out there spend this entire book basically out of sight entirely is distressing; I get that we have to settle our home solar system's story here, but Jesus Christ do I hope that the final trilogy takes place amongst these new worlds already (I know the first book is already out and thus I could already know if that's what's going on, but I'm saving the entire final trilogy to binge on once it's all released, inshallah).
So, while not quite as cool as the first trilogy (Marcos is no Miller in terms of being Holden's primary foil), Babylon's Ashes does a solid job of fulfilling the usually-difficult mission of wrapping up the middle act of a series. If you've enjoyed the series to this point, I doubt you'll not enjoy this entry as well.