It seems that the more reviews an author has for a book, the more it may gain sales or whatever. Even putting a good book at a low or Free price doesn't last with high sales.
Reviews are important, and it only takes a few seconds to write a few words. Yes, there are reviewers who write paragraphs, and some write out the entire plot, but there are those who don't write anything.
I personally have my own review blog, but I never write a bad review. If the book is something that I don't like and would not be able to write something good about it, I inform the author (most of my reading is done by requests) or I don't write one.
As an authr, I've gotten good and bad reviews, but the most painful ones are those who criticize my writing style. Or make it like I should never have written.
If you read a book, and you like it, tell the world. Give the stars and write a few short words.