I've got a confession to make. More often than not, when there's a deeply religious character in a sci-fi novel, I find him/her annoying, not likeable at all. I don't know why. I'm not religious myself, but I've got nothing against faith (just the opposite, I envy who has it). I just don't like that kind of character. Abaddon's gate has one of those characters but surprisingly, I liked her a lot. Probably it's the best among the new characters introduced in this novel. She sees life in a different way than myself, but she's someone I'd love to spend an evening talking to, because she's deeply spiritual but not blinded by her beliefs. See? It wasn't that difficult to write a likeable, religious character.
That said, abaddon's gate is a very good addition to the saga. Plot finally moves significantly ahead, opening up a really interesting scenario to exploit in the next novels. Writing is solid, character very well portraied.
If I really have to find something to complain about, there's a kind of fixed structure in the expanse novels that somehow annoys me. There's an initial part to introduce the new characters, a second part where the main plot is delinetaed, then a tension buildup that culminates in a final gun-blazing act. I really do not feel the need to be so strict about structure. Otherwise, a very satisfying read.