I've been doing a lot of reading via the freebies at BookBub. On a rare occasion I'll purchase one, but it has to have both a good cover and a great pitch.
Unfortunately, I've found very few that I can finish and even fewer that I would recommend to another reader. I've thought of writing reviews for them, but hate to be dishonest. I can't say they are great when they're not, yet I don't want to be a troll and crush someone's dreams of being a writer. It's a dilemma.
The greatest consistency I find among these books is that the author has published too soon. They all need work. From the basic plot line to the characterization to typos, grammatical errors, and poor formatting. Every single one I've read has a least two of the above mentioned.
I'm not great with grammar myself so if I notice the errors, I can only imagine what the Grammar Nazis think.
One I read, actually had ten pages which were repeated twice in a row. I believe that is something an editor wouldn't miss if it had been professionally edited.
A lot of what I've read are common mistakes made by beginning writers. I know this because I've made them myself. I've made them, but didn't publish them.
Rather than turn off my future readers, I've chosen to wait, to put the manuscript away and re-edit it after I've forgotten about it. After I've fallen out of love with my own words.
Russell Blake writes a great post about his reluctance to write reviews. You can check it out here.