I loved The House in the Cerulean Sea. 
This book is a sequel and sadly doesn't live up to the original.
I'm glad we have Klune's voice. He dedicates this book to trans people and in the afterword says he wants to be the anti-J K Rowling.

I guess this book wasn't for me because he tries to provide hope in a way that I don't agree is accurate or possible now. I thought he was very effective and affecting in House, but I just don't buy it here.
I enjoy our main characters and enjoyed spending time with them again.
The ending

just is too much of a deus ex machina. If you have powers like Zoe does, why would you not have used them earlier. Would there have been enough change that the people on the peninsula actually have stood up for the islanders. If you believe you're protecting the world from the antichrist, wouldn't you go even further and attempt to nuke the island.

It just felt too polemic and too easy at the same time.

It may also just be that I'm in a really pessimistic phase. I've been attempting to read In the Lives of Puppets for quite some time and it hasn't grabbed me.