I’m very hard on the books I read. Not physically, because I hate books that are anything less than pristine. But I’m hard on them in that I am very stingy with my ratings. On Goodreads, my average rating is 3.73, which has actually gone up over the last few years. I take that to mean I’m better at picking books, but who knows. Typically, if you are reading on topics that interest you and have done good research on a book, you should read very few books that you would consider to be below average (i.e. below a 3-star rating). But when it comes to differentiating 3 stars versus 4 stars versus 5 stars, the ratings are fairly arbitrary.
I only rate books 5 stars if I feel at some point in the future I want to reread them. That means they were impactful enough that they need multiple reads to take in, or that they were just that enjoyable.