Amazon reviews are hugely important for authors.
Here are a few reasons why:
Amazon gives preference to books with more reviews. The more reviews you have, the more importance Amazon gives you in its recommendation engine (the algorithm that controls the "You might also like this!" and the "Here's a hot new title you might enjoy!"). Based on my own work, it seems like 50 reviews is about the magic number where Amazon starts to really help push your book, with increased efforts at 100 and 200 reviews. This is pretty huge, because it means your one review has a real and measurable impact on the success of the book.
People like a sure thing. We like to know what we're getting for our money. The more good reviews a book has, the more confidently we can be assured that the good is worth our hard-earned dollars.
People trust you. If I tell folks my book is great, they'll say, "Of course you think your book is great, you wrote it." But if you tell them it's great? Now that's a recommendation they can get behind.
Authors need feedback. We always think the books we write are just the best. But if there are glaring plot holes, weak characters, terrible grammar mistakes, or boring storylines, having those pointed out to us is an important part of the whole "do it better next time" process.
Pro Tip: Don't be scared. Your reviews don't have to be grand or sweeping. They don't have to read like a New York Times piece. You don't have to spell all the words correctly or use proper punctuation or write complete sentences. You just have to write something. Even a simple "I liked it, it was fun" will do!
Feeling inspired? Then head on over to Amazon and leave a review for a book you love!