My first impression of this book is that it's much darker than The Warrior Heir. The bad guys in this book are REALLY bad and they have the upper hand for much of the story. While this raises the stakes for Seph and his friends, it also shrouds the story in a sense of foreboding and hopelessness. The decisions faced by the good guys in this story carry major consequences. Seph and his comrades often appear to be painted into corners. Even the end of the book isn't as "hopeful" (if that's the right word) as the ending of the first book.
That's all to pave the way for the next book, The Dragon Heir. The pieces are all put in place for a major showdown amongst various factions of the Weir in the third book and, although the characters are given at least a temporary reprieve from conflict at the end of The Wizard Heir, there are obviously major battles brewing on the horizon. In many ways this is a typical "second book" in a series in the sense that there's not a powerful sense of closure because the stage is being set for the big finale. But there is at least enough closure for Seph in his personal journey that the ending feels satisfying and the reader isn't left feeling cheated out of a fully rounded storyline.
So now I have to go read The Dragon Heir. Still loving Chima's writing.