Books are not judged so much on literary merit, as on appeal to today's middle grader. The scale is 1 to 5 smiley faces. Here's how it was explained to Boy Reader:
☻ Had trouble finishing it
☻☻ Didn’t dig it, but someone else might!
☻☻☻☻ I’d read a sequel
☻☻☻☻☻ More! Can we download the sequel right now?