The Golden Enclaves – Naomi Novik
“A Deadly Education” was brilliant; “The Last Graduate” was excellent. The third book in the trilogy is merely good. The end of the second book left the story in a bad place: The protagonists have achieved everything they could hope for - escaped the school, banished the monsters - and then Orion abandons El and goes back into the school. This is never properly motivated, and the hand-waving explanation we get late in the third book does not satisfy.
What it does is turn a large story into a small one. It becomes a story about El desperately trying to return to Orion and (maybe) save him, rather than trying to save hundreds of people or even the world. (The human magical world at any rate.) It takes half the book to climb out of this hole - a half book dominated by El whining. There is a long London episode that does not advance the story much.
The second half of the book takes on a larger scope, and portrays El more positively.