Reviews are based on taste and preference. What one person dislikes, another person loves. If someone dislikes a book, that doesn’t make it a bad book. On the flip side, if someone loves a book, that doesn’t make it a good book.
A reviewer may say they didn’t like the book because it was too humorous and they prefer serious works. Reading that, I’d jump on the book because I love humor.
When I leave a review for a book, I try to say why I liked the story. It gives the next person something to hang their hat on. If I don’t like a story, I don’t ever leave a negative review because I don’t think it’s fair to bash someone’s hard work. For instance, there’s an author my mother loves (I won’t name names) whom I detest. And we love/hate her for the exact same reason—she’s super heavy on description. I prefer more dialogue than description in my reading. Does that make her a bad author? Not at all. She’s a best-seller.
Several years back, a book came out where the author didn’t use any quote marks to indicate dialogue. That method totally took me out of the story since I had to go back constantly to see if someone was talking or if it was someone’s thoughts or if it was description. I spent too much time trying to understand rather than enjoying the story. I was thoroughly confused after a couple of chapters and never finished. Did this mean it was a bad book? Nope—he’s a best-selling author.
Why are reviews so important for an author? Well, Amazon ranks your book partially based on the number of reviews. Newspaper reviews help authors get on the best-seller lists, etc., etc. Unfortunately, it’s the ‘famous’ authors (the ones who don’t need it) who get the publicity.
So help an author out—if you like a book, give it a review, especially if the author isn’t a best-seller and doesn’t have a lot of reviews. It can be short with just a mention or two of what you liked. You don’t realize how much they’d appreciate it.