I thought the characters were well written. I enjoyed being surprised as to why the main character, Skye, was starting to notice changes in herself. I found it refreshing that we didn't get to find out what was going on with her right away, or couldn't tell what was happening to her right away. Asher and Devin are the two angels sent to look out for her and the two were mysterious and not your average angels. Asher is more of the 'bad boy' type, however Devin could be bad when he wanted to be, and Asher could be sweet, gentle, and kind when he wanted to be. I liked that it wasn't all or nothing with each of them.
I do have to say I'm a bit tired of the "missing parent" in a lot of YA books. Skye lost her parents when she was only 6 (this is key to the storyline) and her "aunt" takes care of her. But, guess what? Her aunt is amazingly gone most of the time on business trips. Now, I will say that at least when her aunt was home she was very well attuned to Skye's life and was interested in what was going on. I just feel like sometimes authors make it easy by making a parent figure absent. Just sayin'.
Overall I liked the book and I will be reading the sequel when it comes out. If you like "fallen angels" series and are looking for a bit of a new twist, this might be your book!