Alone, the the star system is a flawed way to review books. Just simply providing a star rating on Good Reads or Amazon, especially when it is below three stars is bad, bad, bad. One should state why they didn’t like it, because my reasons for rating a book bad will be different than yours.
Ratings really are funny things. They can be good / bad depending on how close one is paying attention and also can be affected by mood. But, they shouldn’t be. As a reviewer, this is to be addressed.
However, so forth and so on, the star rating is a good way to sum up your rating at a quick glance. Also, when coupled with an evaluation and a recommendation makes for a great review.