This book is like the ur-Manic Pixie Dream Girl book, and the narrator is a self-absorbed, mostly unlikeable toolbag, and the author clearly acknowledging all of that only goes so far in redeeming the book.
It's Garden State and Elizabethtown mashed together and set in high school with an extra dose of tragedy/mystery, and I just wish the author had done more than have the narrator acknowledge how Manic Pixie Dream Girl-y he'd set up the Dream Girl to be, acknowledge in the last pages that she was her own person with her own issues that had nothing to do with the narrator. If he'd played with the trope a little more, I might've forgiven the book more for having to spend the entire time in the head of a Nice Guy(TM).
All that being said, John Green can, in fact, write. I just wish that most of the awesome weren't confined to the sidekicks, who once again wildly, wildly outshone the main characters in interest and charm. Sigh.