I might be taking a break from writing, but I haven't taken a break from thinking. ;-)
Moreover, books can't be evaluated like cars and appliances. Their worth can't be conveyed on a scale of one to five. Reading, like sex, is a highly subjective experience. The only way to express the nature of that experience on a reader-by-reader basis is through words. WORDS. (Can you imagine people slapping stars on each other's genitals following an intimate encounter? Heh.) At least Amazon requires you to post a review along with your rating. I'm still not sure if the book must be a "verified purchase" or not, but their system is far preferable to the way Goodreads does things.
Serious readers want and need honest reviews, not mere ratings and certainly not juvenile games played with icons. A review can be a few words long or a few paragraphs long. One needn't possess the vocabulary of John Updike to express one's satisfaction or dissatisfaction with a book.