0-7 Ghost was an amazing read, and I don't think there will ever be quite another story like it. I finished the whole series in a week, and emotions those little books caused... Man I was in a funk for weeks. But it's a beautiful story about the meaning of death and defining the purpose of life(a topic we can never define because it's so personal for each person). It came to me in a very hard part of my life, as I myself was struggling with loss and it really helped me work through those feelings.
Long story short, it's an amazing read, I can't recommend it enough.