As someone with chronic health issues and family members that have had cancer, I really, really liked this book; for the most part. I would say, the first 2/3 of the book are about cancer and what that means even when you do beat it. Continuing life after chronic illness is an odd thing, and I really, really loved that part. I would tear up sometimes over certain parts, especially in the letters to Aunt Sue.
The last 1/3 lost me, though, as it shifted from being about Susan, her relationships, and life to being mostly business focused. -- It doesn't help that their family is clearly well off, being able to afford cancer treatment even after her father is laid off. Then being able to do what, from how it's written, was not a very profitable business for a while.
It went from being such a personal and lovely book to something very, impersonal, and almost odd in comparison to how it started.