Yes and no.
I loved the writing style of this book, and I was very drawn into it. Nathan's a great character, and I love his voice.
However, there were several elements of this book that bothered me:
1. The shallow good-vs-evil themes: White Witches are the "good" witches and Black Witches are supposed to be evil, so of course, the author spends the entire book pounding the evilness and cruelty of the White Witches into your head. I suppose it was meant to be an observation on the nature of good, evil, and hypocrisy, etc, but it left me unimpressed.
2. The secondary characters: Many of them are quirky and fun to read, but none of them are well-developed. This is especially true for Annalise, whose entire role in the story can be described as "token angelic love interest."
3. The ending was too rushed. I supposed I might have cared more if any of the secondary characters actually had more than a single token personality trait, but as it was, I had very little reaction to it. (Though I did love the final scene.)
4. Come to think of it, there really wasn't much of a plot. The first half of the book was torture porn and backstory, and the second half was a series of weird secondary characters, some glossed-over action, and a LOT of buildup for the sequel.
Overall, this was a very readable book, and I think a lot of people will enjoy it. And while I wouldn't call myself "invested" just yet, there was enough this book did well on that I'm willing to pick up the sequel.