The purpose of reviews is to let customers, or readers, know your opinion of a product. In this case, that product is our written work. It doesn't matter if it's a full length novel, a novella, or a short story. What matters is that you, as a reviewer, are giving your honest opinion of said product. But some indie authors are under the impression that the only reason anyone should ever write a review is to give them glowing praise. If you, like many indie authors, also review books, you have great potential for coming under fire by other independent authors.
Let's say that you come across a novel that is on a freebie weekend through Amazon. Because it doesn't cost you anything, you figure you'll give it a shot. After all you can't go wrong with free, right? So you take your time to read through said novel, and while the plot is engaging and the characters interesting, the editing [or lack thereof] is positively atrocious. It takes you a week to read through a 200 page book, not because you didn't have enough time to read, but because you felt like you were having an aneurysm and your eyes were bleeding every time you read for more than 10 minutes. Because of this, you leave a 3-star review. If you look on Amazon at their definitions of each rating, 3 stars means "It was ok." Not the best thing you've ever laid eyes on, but not the worst either.
So, to be diplomatic, you do what any good reviewer should. You give a few positive things about it that you enjoyed, and you also bring to light that someone with better eyesight than a field mole should have edited the piece. And now, if your Amazon reviewer profile states that you're an author, the shitstorm begins. You'll start noticing sudden, nasty reviews or messages on Goodreads, Facebook, and whatever social media you're a part of. Because these indie authors are used to people throwing unwarranted praise at their feet, they don't know what to do with a genuine piece of critique. "It's bashing! Bullying!" etc etc, blah blah blah.
...Seriously, folks. We're not eight years old on the playground anymore. An intelligent adult just gave their honest opinion of something you wrote. If they said something you didn't agree with, it's probably in your best interest to suck it up, pay more attention to what they did like, and move on. I think I received a 3 star on "Lunacy", and the reviewer wasn't a troll who said "You suxx0rs, u r teh crappiest righter EVAR!" No, she actually pointed out a few things about the work that were bothering ME, the author, so my hopes that readers wouldn't pick up on those things were dashed. It's actually what urged me to do the final revision I'm working on, at the moment. And even though there were some things she didn't like, she still complimented a few parts.
My point, through all this rambling, is this: don't be so damned thin-skinned, fellow indie authors. Some people will love you, some people will hate you, some people will only find your work mediocre. A middle of the road, or even BAD, review isn't something to start a war with the reviewer over. Grow up.