There is a certain GIS related book that I'm thinking of purchasing. Unfortunately, there are no comments or reviews on sites such as Amazon of that particular book.
Are questions asking "what do you think of this GIS related book" acceptable on GIS.SE?
A question like "is XXX book a good introduction to YYYY?" might be better worded but I'd be happy to see this sort of question (as a community wiki).
No, not really: the question asks specifically for opinions, which is explicitly off-topic. That's not something this community can even argue about as long as we remain part of SE.
However, often such questions can be rephrased to probe for useful, objective answers. For instance, if the book is (hypothetically) about learning to use Python for automating ESRI products, you might ask about how this book compares to any others devoted to the same topic and why.
One advantage of taking care to craft an objectively answerable question is that you get better answers and often will be (pleasantly) surprised by the emergence of unexpected answers (like, "yes that book is good for beginners but XXX would serve your needs much better").
One aspect of obtaining objective answers consists of taking some care to stipulate what you mean by potentially subjective characteristics like "good." A book that is "good" for one person could be terrible for another. State what needs the book is intended to satisfy: what level should it be written at? What things should it teach? Otherwise we are left dealing with a question that is not only subjective but also vague.
