What I liked most was Croaker's voice. His first-person narration really carries the book and tells you how to feel about the characters and events; he's a sympathetic voice from inside the camp of what, in most fantasy novels, would be The Enemy. And he makes you like the enemy, and want them to win.
It sounds like a simplistic thing to do, but it's really not. It requires the writer knowing his narrator from the inside and not slipping out of his voice for an instant, because then the reader's belief will slip. Everything has to make sense; there's no hiding in this kind of narrative, except of things which the narrator does not know. And of course there's the issue of dishonest narration: looked at one way, the entirety of The Black Company is told dishonestly, since a convention of epic fantasy is we're "supposed" to root for the Oppressed Good Guys. But I don't think Cook did it that way; he was more ambiguous.
The Lady summons Croaker so he can see events and record them as they happened, even if it makes The Lady look bad (or so he thinks). Now she could be taken as an ultimate dishonest narrator, but she does not appear to lie to herself at any point; she only lies to The Taken and the Rebel. She, though, must know that any written account is by definition told from its narrator's view of truth.
Croaker himself says that he will sometimes sugarcoat events when he writes them in the Annals; and he forgives many things of his "brothers" in the Company, to whom he feels loyalty above and beyond that to anyone or anything else. Forgiving is not the same as not seeing; forgiving implies that he does see things, and then forgives. He says at the end he is no longer in love with the idea of The Lady, and proves this by trying to talk The Captain into leaving her and taking the Company with him. Because he does not feel loyalty to her, does he then not sugarcoat her doings in the Annals? We don't see the Annals. We see his narration in the book we are reading.
[I begin chasing my tail.]
I stayed up last night to finish the book, partly to find out if any of my favorite characters were going to die (they didn't), and partly to find out if I'd been right about Darling being magic, which I was. I'd guessed long before Croaker did, but possibly not as early as Raven was supposed to have done. I didn't guess at all about the sneaky stuff involving the Limper and his fake-banishment.
It seems that The Lady won, but the threat of the Dominator is not erased. Hence books two and three in the trilogy, I suspect.