In a book targeted at a teen audience the language, the action, the thought processes, the drama, the angst of the characters, and the style of writing and presenting information are all going to be (or should be) geared to the tastes of teens - NOT adults. My students are increasingly more sophisticated in some ways, but their life experience and exposure to history is still quite limited when compared with that of most adults. Certain plot twists may seem obvious to an adult, but to a 13-year-old they may be fresh and unexpected. Short bites of information may seem lacking in depth to someone with background knowledge of the subject, but to those for whom this is new information it may be the right amount for them to process.
I am not saying that there are not books deserving of low ratings, but to knock them for catering to the intended audience seems unfair. While adults may read and enjoy YA fiction and non-fiction, they should be mindful that young adult books are written for young adults and in my opinion, should judge books through the lens of the those for whom the book was written.