Cibola Burn, the novel that Season 4 was based on, is generally regarded as the weakest of the novels. The new characters are largeley flatly drawn, with Murtry given no development or motivation beyond 'mustasche twiddling bad guy'.
I think the TV show adapted it into something that far exceeds the novel. The Ilus plotline (which is the whole of the novel) was given a lot more pace, devlopment of Miller's 'Investigator' character, Amos' relationship with Wei (another cipher in the novel) and at least Murtry is seen to be disillusioned with his progess in RCE, and a profiteer. The effects of gravity on Naomi were also well portrayed in 'show not tell' the Belter's problems at the bottom of a planetary gravity well. In the book she stays on the Rocinante.
Of course we also got all of the other good stuff with Bobby (partly adapted from the novella Gods of Risk), Avasarala's political struggles and Drummer & Ashton's conflict with Marcos Inaros (brought forward from the next novel Nemesis Games.)
For me, the show frequently improves on the books (Drummer & Ashton are both minor characters who don't much resemble their TV counterparts. At this stage (S4) Drummer hasn't even been introduced in the novels.)
I was really worried about S4, given the weakness of the book, but though it's still probably my least favourite season, I think they knocked it out of the park considering the source material.
