Satisfactory and extremely long. Years ago, I liked the first Expanse book that I read, but I did not think it was anything too great & so I decided to not read any more of these door-stopper novels. Then the TV series came out, and year by year my affection for the series and its characters gradually increased. And so when it came time to queue up some new audio books, I decided to listen to these next. As above, they are consistently OK. The real star of the books is the world building, for which the best adjective I can come up with is "solid". The books are set a few centuries in the future as humans have colonized the solar system, and they don't really rely on any extraordinary new technology. The one conceit is that people have discovered an extremely low-fuel drive which allows them to perform low G burns basically indefinitely. With this efficient drive, Mars is a few days away, while Jupiter and the like are a matter of weeks or months. Other than that change the author sticks to technology that is entirely within our current trajectory and does not require any great leaps. (if anything this is a bit unrealistic, since you would expect changes in AI/bio-tech to significantly upend things. However does make the rest of the reasoning easier if you assume these techs make incremental rather than revolutionary developments.) So despite taking place in space, the series feels very grounded, as basically everything that occurs in space would be understandable by an ISS veteran or the like. And the author does a ton of exploration of what it would mean to live and work in space when you don't have Star Trek levels of technology. E.g: gravity is a big deal; it's intelligently worked into how the ships are designed, it changes how people look and develop & their cultures, it affects everything about life on board a ship depending the ship is at 0G, .3G, 1G, or 5G, or 15G. The authors try to think about all the little things in life, like the sound of the hand-vac that you use to clean up the blood spheres that form after an accident in 0G, the plants and filters needed for life support, the difficulty of developing genuine food growth and eco-system webs outside of earth & the logistical and strategic implications thereof, etc etc. There's just a ton of work done by the authors to present reasonable and interesting solar-politics and strategy and logistics and culture and bio-systems. It's not genius stuff like Banks would make, and there are holes if you decide to poke too hard at it, but despite those minor quibbles The Expanse is the most well-realized version of the 2300's that I've seen.
Now for the downsides. The audio-book narrator is not doing these books any favors. He is for the most part very calm and neutral, when he should be doing emotions and silly voices. The books themselves are also too long. For the third book, the TV series just flat dropped the events from the last third of the story, and they were 100% correct to do so. Like the book's editor could have just excised 200 pages from the middle of the story and things would have been fine, nobody would have been disappointed. (*Edit*: wait, no, on re-watch the TV series *did* have these episodes, but I had skipped them in the TV show as well as the book since they were so un-needed & then scrubbed them from my memory. My bad!) There's also some weird narrative clunkiness and what I can only describe as plot elongation, where the chain of events and logic in the first book is stretched to absurd lengths (TENET syndrome). This sort of stuff only makes sense if the narrative was assembled from the emergent randomness of an RPG group rather than being designed and plotted out beforehand by a writer.