Honestly, I loved this book. It made this series become one of my favorite things I've read all year.
I get why a lot of people were disappointed with this finale, I agree things were rushed and resolved way too quickly and easily, however, that was exactly something that I expected, all of the other books in the series had a similar problem, the only one that did it best, in my opinion, was The Cruel Prince, which happens to be the biggest book in the series.
Overall, this series isn't the best plotted, but I love the characters and their relationships that it just made this whole book so amazing because we finally got some development with them, especially Jude and Cardan.