I was very impressed with this book and it is almost, but not quite a five star book. It is certainly the best of Steninbeck's books and he himself saw it as the culmination of his work.
It is mostly a meditation on good and evil drawing heavily on the book of Genesis, but it is also about family, loss, guilt and the absence of love.
It is written in a very smooth manner and the characterization is both naturalistic, but also has a feeling of a fable or an epic. I think that it would be clearly superior to The Grapes of Wrath. It didn't feel forced to me as Steinbeck often does. Good work and I would recommend it. A very pleasant and lovely read.