So, why not five stars?
I felt...just a little let down by it. I felt like there was just something missing from it. Shai and Gaotona were both wonderful characters, but everyone else seemed maybe a little simple. And as much as I loved Shai and Gaotona, I wish I'd had more time to get to know them. Shai is so insightful, she pretty much had Gaotona figured out by his second or third appearance, and we didn't learn anything more about him after that. And Shai...spent a lot of her time talking about the ways she'd change herself, but except for a few root opinions, her diligence, stubbornness, and her Forger training showing through, there wasn't a lot to her. Nothing about her family or history or anything.
The book was short, and honestly, Sanderson squeezed in an incredible amount of characterization, what with everything else that was going on. But most of the book, Shai spent sitting in her room or talking about the magic system or analyzing the personality of the Emperor,
Also, as great as the magic system was, it....was never really explained to my satisfaction. I have some trouble deciding what would work and what wouldn't, and where and how and why and when. Even Shai is sometimes confused by it.
So, I enjoyed the book very much. I just felt as if there could have been a bit more to it. Maybe I'd feel more impressed if I'd read the other books connected to this one, but The Emperor's Soul read as a standalone, so I'm not sure. I'll just have to go read them and find out.
Oh, but look at that cover! It's inaccurate - if it's a picture of Shai, she's supposed to wear glasses - but it's so beautiful.