It's marked as YA only because the main character is 15, I think; the story and writing feel a lot more suited to the 10-12 age range, as long as they can tolerate the crush-iness between the main characters (don't worry, no make-out scenes).
Interesting main concept: characters in books have lives of their own after the cover is closed--kind of like 'Wreck It Ralph', only you can never leave your own game/book. Every time the book is read, the characters must go through the motions of the story all over again, but once the book is closed, this villain is actually a nice guy with a geeky hobby, those boy-crazy characters actually don't like men, and (in this case) the hero is tired of the endless repetition and wishes he could get out of the book. When one reader (who only wishes she could climb INTO the story) develops a fictional-character-crush on the hero-prince and starts repeatedly re-reading the story, the prince finds a way to speak with her and they both try to find a way to get him out of the book.
Fast read, fairly simple story, and a bit of fun with the real/private personalities of the different fairy tale characters. Nice, light adventure. I share other reviewers' irritation with one brief point where the protagonist notices certain characters dislike men and thinks 'omg, they're hard-core feminists?!'--I had to facepalm a bit there; that doesn't make you a feminist, it just means you dislike men. Other than that and a couple of plot choices (like the fire extinguisher--what the heck was that?) that I think only confirm this book's rightful place in pre-teen rather than YA shelves, it's a fairly decent casual read.