I really enjoyed the further character development of the Night Court, the tricky intrigue, and learning more about the world and creatures in it. As for the main plot, its mostly a series of power ratcheting. Hybern gets more powerful, then our fairys get more powerful. There's also extremely little sacrifice for such a world ending, overcoming-impossible-odds war. Sure, its filled with death, but can you imagine any of the main characters dying? I would have been devastated of course, but for the size of the court, the level of protagonist immunity is a little absurd.
I did learn one valuable lesson however: When hope is all but lost, maybe check you local library for any ancient all powerful monster. I love that library omg.