I got this book in 2007, when I really wanted to color but adult coloring books didn't exist. I finished the bones and muscles that year. I used those pages as a reference over the years to look up sites of injuries. This year, after an offhand comment by a doctor, I picked up this book again and I'm working through the other systems. (So far, I've done the nerves, digestive, respiratory, urinary, and lymphoid systems. I'm leaving cardiovascular for last because it looks boring ...).
I have no connection to medicine or health care, except of being a patient. This book has served my various purposes - coloring without feeling like a five-year-old, reference text, making myself less stupid, confirming that I could never be a doctor, occasional insomnia remedy.
Coloring issues:
I wish the letters in the titles were thinner, so that I could just color them in by writing the word normally instead of having to back-track over the letters. It is frustrating that it advises "light colors" for so many structures. Medium colored pencil colors will show the details within the structures. The paper is thin and absorbs a lot of ink, so most of my markers end up looking "dark" (for instance compared to the Johanna Basford Secret Garden series). It is good that each page is printed single-sided, though I still have to put an extra sheet of paper behind the current page to prevent markers from bleeding through to the next sheet. And this is probably just me, but I spend a lot of time planning which colors to use, especially for the lymphoid system which has the same types of cells repeated for several pages.
I don't remember finding any errors in the bones and muscles section, but there are a couple in the rest of the book. For instance, in the nerves of the eyes, there is a layer of cells labeled "S" but there is no title associated with "S". Sometimes the coloring instructions say to use a certain color for "J" and there is no "J" on the page. I would say this book is clearly designed to be used as a supplement to other texts, because the text in this book is not self-explanatory (no definition of "peristalsis," for instance).
I'm not the target audience for this book, but I still get good use out of it.