I rate books according to the following general guidelines:
I really liked this book while reading it, but I probably wouldn’t read it. It had some impact on my life.
This book was okay. It didn’t alter my life in any way.
This book was not for me. I had some significant issues with it and did not enjoy it.
I really disliked (borderline hated) this book. I had nothing but problems with it.
If it impacted my life, it was completely negative.
Please note that the 5 stars given to a romantic contemporary YA are very different than the 5 stars given to a non-fiction history of psychology, for instance.