This is a favorite. I'll have to see how it ranks for me among Poisonwood Bible and Prodigal Summer after I sit with this awhile. I didn't know if she could top Poisonwood Bible.

She makes the character's specifics - where he was born, in foster care, with opioids, with death of his parents, friends and dreams into universal struggles we all can relate to. The plot moves along and hooks you again at each turn and the ending is tied up just enough but leaves plenty to chance and imagination.

Other thoughts:

Home and the draw of a place where you're known, but also as a place you need to leave. I feel like everyone's got a literal or metaphorical experience like this. 

The harsh critique of systems and loving care for individuals in DSS (and other places) was done masterfully, contrasted through several characters. 

I can't say for sure, not being from the mountains, but I hope the Appalachian aspect was done respectfully. A few characters (Tommy, June) even analyze the situation for the reader in case you aren't familiar - could give some folks a lot to think about. For my part, I felt the characters and setting were more than stereotypes - they are the heart and you're on their team. She's even incorporated local quirks like the use of whenever in place of when and other area specifics like a discussion of Melungeons.

And, as usual, Kingsolver evokes the natural world so vividly you'll be disappointed you're aren't really there in the woods when you look up from the book.