I’ll go into detail later but I want to mention one fact right away; the gold at the end of the rainbow is that YOU CAN CHANGE YOUR MIND AND HOW YOU THINK. This is called neuroplasticity. Your genes, hormones, regions in the brain and early learning do not necessarily determine your fate.
If you don't have even a slight sense of gallows humour about your depression, this is not a book for you.
If you expect an introduction to mindfulness, you will also be disappointed; this is a why-to, not a how-to book. It simply recommends, in one sentence, taking an eight-week course in mindfulness (you can also find a few good free, no-registration courses online), and gives you some exercises.
What is does is to explain the brain processes behind feeling shitty about oneself with precision and clarity; if rational arguments work for you, this book can really be a lifeline. Also, it finally convinced me to start studying mindfulness, as opposed to numerous books and articles I've read over the last three years, so this *is* something.