From the beginning, then, I wondered whether Charlie could be trusted as a narrator. What details were true, and what did he change to maintain his secret identity? I also kept trying to figure out who he chose to receive the letters, as this person's identity will reveal something about Charlie.
Anyway, I'm not done with the book yet, so I'll let you know if I like how it all turns out! I'm definitely intrigued, though.
This letter structure, though, reminded me of other books with narration devices that create suspense. Of course, Marcus Zusak, author of The Book Thief and I Am the Messenger, is masterful at shaking up POV. *SPOILERS* Death is the narrator of The Book Thief, which we don't really figure out until the end of the book. And I Am the Messenger has an interesting twist where the first-person narrator learns who is really sending him messages that are shaping the course of his life.
Rebecca Stead's When You Reach Me is written in first and second person ("I check the box under my bed, which is where I've kept your notes . . ."). Again, the "you" isn't revealed until the end, which ups the mystery throughout the book.
Have you seen any other interesting narration or point of view devices?