The Expanse is based on a book series by James S. A. Corey (authors Daniel Abraham and Ty Franck), which I haven't read yet, but I have the first one on my list. From what I've read from those who have read them, the plot roughly sticks to the books, though sometimes bits are changed up, such as a character's motivation, or which character did what when. I haven't really seen any complaints, and have even seen some people comment they think the show is actually tweaking characters and plot points to make more sense in the big picture. Which I guess makes sense, because the show writers have the advantage of knowing exactly what happens in future books and can plan things out accordingly.
The cast of characters have nice representation, both according to our present-day standards, as well as the future standards in which the governments of Earth has colonized much of the solar system. The three major powers are Earth, Mars, and The Belt, in a very delicate state of being on the verge of war. The push comes when the ice hauler The Canterbury receives a distress call on its way to the colony of Ceres, and spirals out a conspiracy that threatens humanity itself.
Here's a teaser for season one, to avoid spoilers if you haven't seen it:
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Let me introduce you to Head Bitch In Charge and Fashion Icon, Chrisjen Avasarala (Shohreh Aghdashloo), who drops swear words like candy. For the SyFy airing, they edit the F-bombs, but that's about it. I watched season one and two via DVD, so I heard it all, but I'm watching the current season three on SyFy.
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If you're in the US and have Prime Video, you can watch season one and two for free. I believe it's on Netflix in the rest of the world. If you haven't given it a try, I highly recommend it.
The first season had a lot of "futuristic noir detective" stuff that I didn't think I'd care for, but once the show gets going, it's amazing to see how all the seemingly random bits tie together. The f/x is some of the best I've seen, and they actually attempt to show how artificial gravity would work in a semi-realistic way. From what I understand, they're not doing a direct one-to-one adaptations from the books, but are doing roughly half a book per season, so with 8th book coming out later this year (plus some novellas and short stories), there's plenty of material to mine for future seasons.