4.5 stars 
 Perfectly deserving of the National Book Award 
 The book starts out very disconnected. There is a lot to take in. You have to spend some time with the book to figuring things out. It helps to know a little about the book is prior to delving in: it's a first-person account of a teenage boy's descent into mental illness. In the first few chapters, you will find that Caden is experiencing hallucinations and is having a difficult time discerning between those and reality. 
 The chapters seem so incohesive but the effect is compelling in that you experience the same confusion parallel to Caden's at the onset of his mental illness. 
 Don't give up on the book if you get frustrated -- it'll start to make sense a few chapters in! By midway, you will start to piece together the allegory, so to speak, of the Challenger Deep through Caden's hallucinations, and identities will be revealed through Caden's bouts of lucidity. 
 My favorite parts of the book are the last few chapters. (view spoiler)[Though it ended with a positive outcome for Caden, the book doesn't idealize mental illness. It's confusing and doesn't really go away permanently. It's unpredictable and impacts lives. The perpetual psychology student in me especially appreciate the last couple of paragraphs in which Caden talks about how the Captain will always be waiting and that there's a chance he may go with him again, whether he wants to or not. (hide spoiler)] 
 It's a tough read in terms of the heaviness of material, but otherwise the chapters are short and the imagery is vivid; I had to take breaks throughout the book to allow my mind to digest and absorb the descriptions. I 100% recommend this book to anyone who enjoys a challenging, realistic, and honest book about complexities of mental illness.