I know this book is well-loved (currently averaging a rating of 4.32 on Goodreads) but it just didn't hit me the same way. It's not that I don't cry reading books (I absolutely do; most recently, Jason Segel's Nightmares! left me a weepy mess), just not this one. 
 (view spoiler)[I really liked the writing, and the monster's stories in particular, but I was not strongly saddened or otherwise affected by the story overall. There was certainly sadness in Conor's life, but the contrast shown in those sad aspects was so slight that it was hard to experience the loss with Conor, often because it had already happened. You just got to swim in the present misery with him. Friends became less close, bullies became crueler, but nobody dramatically switched categories. His father was either absent or inattentive and there was no extensive memory of (or hope for) a life with him. His mother died, but we only saw her when she was already quite ill, not when she was really alive and well, the person he would miss; I expect for many readers, this last part is actually a strength of the book, as it invites them to fill in the details with those of their own lost loved ones, and re-live that loss with Conor. (hide spoiler)]