1. There is so much great character development in this book, in major and minor characters alike. At the beginning of the book I continued to want to just smack Shallan frequently, but by the end I wanted to high-five her and cheer "you go girl!" Same goes for Kaladin. But we also get so much more from people like Adolin, Renarin, Szeth, Moash, Sadeas, even Elhokar.
2. The mysteries just keep getting deeper. Just as I think I'm starting to figure something out, I realize there's a whole other layer to what's going on. Part worldbuilding and part story-telling...100% awesome.
3. Backstory! Previously, we were treated to Kaladin's personal history. In this installment, we get to see into Shallan's past and holy moly -- that girl's family is SERIOUSLY MESSED UP. It's no wonder girl spends most of the book with an epic case of if-I-just-ignore-it-then-it-never-happened.
4. Broader points of view. We get to see into the heads of Szeth and the Parshendi and Sadeas. These are not necessarily happy places to be, but are quite enlightening and add to the whole layer upon layer storytelling.
5. Resolution + Questions + Surprises. There are several good twists and surprises in this book. My husband's got the best poker face, since he finished first and then got to listen and nod as I'd talk about the book while reading it. Never gave anything away. Sanderson also does a great job of giving readers some payout on what was set up in the first book -- some secrets come to light, some people have epiphanies, and we get more than one epic showdown of some kind. But, like any good series installment, we're also left with more questions, and plenty of foreshadowing (and foreboding -- things are about to get real in Roshar).