The only way to end the first book in a YA series is to chop it off at the knees, just when the going gets good. It doesn't matter if everything behind it was just build-up to the REAL story. You're not getting that until book two. Suckers.
I don't give books star ratings; I give them bite ratings. This is a bite. A book can get up to five of these evil-looking chompers, including half bites.
You can attribute your own wording to the ratings. Five's the best, three's decent, one and under isn't worth the gas to go to the library. I'll leave it to you to fill in the blanks.