First of all, I'm glad I finished this book: I liked how it ended and it even convinced me to add the rest of this trilogy to my to-read list. It is well-written and the authors took particular attention to the details.
However, I gave it 3 stars because before getting to the last few chapters that I enjoyed, I was about to give up and set it aside few times. Throughout the whole book, I just couldn't feel attracted to the MCs. While they're supposed to be older (she's 19 and he's over a hundred and fifty years old), their dialog was too childish most of the time, and it became annoying. Also, and it's my personal reaction to some parts of the book, I felt uncomfortable reading it at times. Their behavior (PDA, the inconsiderate "mischief," ...) made me cringe inside.
Thankfully, the action picked up towards the end, and the new plot developing sounds interesting! So give it a try!