This is the best YA I've read in a long time, and I've read quite a lot of YA this year. Intriguing retelling of Snow White, mostly believable heroine, likeable hero, a few interesting minor characters, good pacing, adequate but not overpowering world building. Others might have turned this idea into a trilogy with a sagging middle book, but I appreciated that Lewis tells the story well in one full book. We have the exile, the trust building, the return and satisfying culmination. Yes, there could have been more details about minor characters and more world building on each planet, but it would have been unneccessary padding. The main story is told cleanly and well. 
 Essie is a likeable protagonist. I rooted for her from the beginning, and her journey from self doubt to fulfilling her purpose is gradual enough to be believable. The one thing that I found jarring as I read was the cage fighting. She's a cool programming/engineering nerd. She's already breaking most of the Snow White/princess stereotypes, in a realistic way--does she need to be bruised and bloody, too? This was the one element of Essie that seemed derivative (Katniss or Tris get bloody, so that's what YA heroines do nowadays) rather than original. The cage fight at the beginning of the book did draw me in from the first page and made me want to find out more about her, but the further in I got, the less the Essie I was getting to know (the girl who had been hiding for eight years and was better with computers/electronics than people) had anything to do with that fighting Essie from page 1. 
 I enjoyed Dane and the fact that their relationship is not insta-love but also not as tortured as the love triangles we see in so much YA. The pace of their growing trust and affection was refreshing. I liked that they were evenly matched, with common skill sets (his programming of her droids was funny) and struggles with the destiny they were born to. I did find it odd that (view spoiler)[Essie's dad and Olivia allowed Dane to stay with her once she returned to the palace. If her dad is the monster implied in his final scene and Olivia is out to murder her, why would they let a stranger stay on as her personal guard? I just didn't believe that they'd be all hunky-dory with Dane instead of insanely suspicious. (hide spoiler)] 
 Others have mentioned the one really dark plot thread that is revealed regarding Essie's dad. It does make sense of a lot of her reactions before that, but it is pretty dark for a book that otherwise mostly steers clear of profanity, sex, and torture. I'd hold off recommending this to younger YA readers because of that. 
 I enjoyed the world that I entered with Stitching Snow. It wasn't what I expected, but I wouldn't mind visiting this universe again.