Okay, first of all I was apprehensive to read this to say the least. I remember the previous book was very Celaena focused, by which I mean it was as if the author was fan girling her the whole time. Not to say that that affected my opinion of the book, just how much I took it seriously. This book had way more depth. 
 The characters were the biggest improvement in this book in comparison to the last one. They had a bunch more depth whereas before they were all stereotypes and very obvious. It's kind of like speaking to people you haven't spoken to since secondary school and then seeing how they've matured and become realer people (not saying say that school people aren't real or anything) 
 The plot as well though- dude- I was doing that thing that I haven't done in aaaaages, skipping a few pages forward to see what would happen and then going back and reading up to it. That was how much suspense there was crafted into this book. 
 Everything about this book was so much more polished. The emotions were way more realistic, the choices so much more difficult and the plot was full of twists and turns.