I recently read and reviewed the companion sequel to this book, Huntress, which is coming out in April. It doesn't matter which you read first, because they're just companions.
As much as I liked Huntress, I think I liked this one more. It's a twist on the popular fairy tale Cinderella, and it's just so beautifully retold. Once again, Malinda Lo creates a gorgeous world with her words. Along with this Cinderella story, there's a completely different side, that involves fairies, especially one called Sidhean. He's such an interesting, mysterious character.
When Sidhean's on the page, the scene is typically dark and mystical. Opposite him is Kaisa, the King's Huntress, who is warm and sunny. I love how the two contrasted... it makes two very different sides of the story.
I recommend this book to any romance or fantasy lover, especially if you love fairy tale re-tellings.