I only just finished this book. I liked it.
I love Sam and his grandparents and his mom. It felt like reading about my friends... Sadie, I'm ambiguous about. I think she's a genius and I feel sympathy for her in many instances, but I do not love her, as a person... Which is ironic, since I recognize a lot of my former self in her (not the genius part, sadly). But the person who broke my heart and made me want to cry and throw myself to the floor while reading this story... has to be Marx. The NPC who ended up being the main character for me... There's no heartfelt story without the NPC, the tamer of horses.
I'm definitely rereading this one in the future. There are more levels that need to be unlocked.

Next level unlocked: I have to say, bookclubs are the best way to broaden your horizon... Now that I know a bit more about the author, I realize I will always try to separate the art from the creator IF I like the art. If I don't like the art or the creator, well, then I don't really care about it anyway. Will I read more of Zevin's work in the future? I'm unsure... But I will always love the work I already read. You can't take that away from anymore!