The novel picks up after the apocalyptic events of the last book which have opened a massive alien portal network to 1500 inhabitable new worlds. Immediately, illegal colonists from all across the system have flooded these worlds followed by more legitimate upscale scientists to research it. One of these planets is Ilus (called "New Terra" by the UN). OPA terrorists kill fifty colonists and chaos reigns with James Holden sent with his crew to make peace. Except, there's more on the planet than either side could imagine.
I've got to say I love the early-established twist that Holden and company are sent to the colony in order to sabotage the peace process. The Rocinante crew have such a reputation as troublemakers that the U.N. believes they'll utterly bone things so that the "Gold Rush" to colonize the new worlds will be delayed. It's such a wonderful endorsement of how big a bunch of screw ups are heroes are.
This is probably my second favorite novel of the series after the original because it returns to the human politics of the setting over the more cosmic elements. There's a strong mixture of Wild West with sci-fi elements that reminds me a bit of Mass Effect: Andromeda's better parts. The colonists are protected by a corrupt but effective small town Sheriff named Murtry while the Belter colonists are much more wild as well as savage. They've decided to make their homes on the planet and anyone who tries to get them to leave are considered invaders, even when the second group obeyed all the forms necessary for colonizing the region.
Holden has matured a good deal from his previous escapades and become a more cautious leader. Even so, he remains idealistic to the point of stupidity at times. Virtually all of his problems would have been solved by shooting Murtry but he refuses to do so. In the end, he's willing to compromise himself much more while keeping his eye on the prize. Basically, he's grown up and become a more pragmatic sort of hero than the mindlessly idealistic Don Quixote figure who I repeatedly wanted to punch in the face.
My favorite character in the book is Murtry because I love the tireless loyalty he has for Royal Charter Energy Company. A lot of people in the Expanse are flexible about their loyalties while Murtry is willing to die for the purposes of fulfilling his contract. It makes him an admirable character even when he's willing to see the colony destroyed. He plays the role of a small-town sheriff who assembles a posse/militia to protect his company's interests and while Holden considers him a monster, I consider his position to be pretty justified after a group of people committed mass murder on his watch. I'd be wanting to hang the Belter colonists too.
We also get a return of Detective Miller's partner and POV character, Havelock, which I felt was a welcome addition. The character was only briefly in the books and not much more so in the show but made a positive impression on me. Finding out what happened to him after Protogen collapsed and finding out he went "full Belter" was interesting. It also provides a human-link to the colonists' feelings.
The kind of crap the colonists go through is tremendous and reminds me of the horrors faced by colonists in the early New World days only exaggerated. There's blindness plagues, toxic slugs, earthquakes, alien technology malfunctions, and conflicts between them. That's in addition to more mundane issues like famine, lack of medicine, and lack of contact with their patrons.
In conclusion, Cibola Burn is a great novel that I enjoyed from beginning to end. I liked the actions, politics, and the characters. The precursor technology isn't really great and takes over too much of the plot but that's just how it goes. Really, I love the continued struggle between Belters, Earthers, and Martians for any new resources we encounter as a species. It's all too human.