but I felt that the characters looked exactly the same as they were 3 decades ago
I felt otherwise. For me, the characters felt more matured and tired/weary. Holden and Naomi making plans for sunset, Bobby wanting to be captain. Amos's lot more mercurial than he ever was. Only Alex kinda felt the same, but then I expect his character to be the same flight jockey even if he dies of old age in the cockpit. The spark that was Hodlen felt extinguished.
Agree on Avasarala. Drummer feels a very weak character to replace the stalwart.
The book felt like a scene setter, building foundation for the events to come. Now I get a strong feeling that Holden/Naomi will die at the end. Maybe Amos too. Bobby and Alex will survive.