Often seen are comments, blogs and tweets regarding 1* reviews on Amazon. Some people think that if you haven't got fluffy things to say and at least 4 stars to give to a book, then you shouldn't say anything. I disagree. Too many Indie writers' first books are touted as 'best-seller' in their promos.
My early novel typescripts are accumulating dust in cupboards and boxes. I had sold many short stories but was still learning the writer's trade (still trying) and although I loved the accomplishment, I knew the books weren't any good. I wonder if the opportunities now available had been around then, would I have self-published the dross? I have the feeling I might have and would now be blushing with shame.
First, second, and maybe more attempts at full-length fiction by tyro writers can be poor. Most will be like the curate's egg. Early imperfections are part of the apprenticeship that a writer must serve in order to master, or at least make a decent fist of, the storyteller's art.
Reading and scribbling from a very early age in your mother tongue is necessary but not sufficient. Most of us walk and run as toddlers but that doesn't guarantee an Olympic track medal.
It is a fine accomplishment to complete your first 90,000 word typescript. It is possibly the best writing you have ever drafted and edited, but it is only a foundation stone for building on. It is the best you can do at the time but better is to come.
These first works are probably worthy of only a few stars, but any reviews, hinting at directions where errors might lie, are worth their weight in paper. Many early, and sometimes hurtful, reviews are vital for the learning process. Hug them to you and learn! Ignore the useless and spiteful.
Write reviews for other writers. Honestly try to indicate where you found the story unsatisfactory, where characters didn't convince, where dialogue sounded false or weak, point out reading stumbling blocks, typos and wrong word usage, everything that stopped the flow and spirit of the tale. You will learn things at the same time as providing your fellow scribe with invaluable hints. If you think two stars are more than fair then give them. Don't feel mean. Your honest, directed opinion is worth a handful of five star puffs from friends and relatives.