This is a tough book for me to rate. On the one hand, I appreciated the double allegory of working through grief, and of the fight of good and evil over the Tree of Life. It was a story that felt rich and heavy in a good way; deep; important.
On the other hand, there is a stylistic your-mileage-may-vary aspect of the storytelling that prevented me from getting into the story -- YMMV because it's something that got in my way but others may like it. Smucker tells the story partly in the present, with the protagonist as an old man, and partly in the past, the summer he was 12, but the old man tells us the story from when he was a kid, spoiling the major events before they happen. I love to read the events of a book as the character is experiencing it. I want to be surprised. I want to feel their reactions as my reactions. But I can't do that if I know the major pieces of what's going to happen and if the storyteller keeps throwing in foreshadowing. It is a report, rather than an experience. I don't want to be told that a character thinks or wonders or feels something; I want the thoughts, the wonderings, the feelings presented without the filter of a teller looking into the past.
That said, I liked the old man's story a lot, especially his relationship to Caleb. And the teaser for the sequel is seriously intriguing; Abra is a great character. For me, I would have preferred the boy's story sections first, and then the old man's, so the boy's story gives richness to the old man's actions, rather than the old man giving away what was about to happen in the boy's story.
So, for me, the story was strong, but the storytelling was not what I prefer -- although others clearly do not have an issue with it.
(I hesitate to mention, but I will, that the book could have used another round of editing to remove high-value words repeated within sentences and paragraphs, and too many sentences in a row that start with the same word. I'd love to see the author do this super-fussy work in the next novel, because he's got a gift, and those details can take a work from good to great.)