KitKatxKK I agree 100% that one should read at least 10 chapters for a review (barring that each chapter isn't incredibly long, 10k+ word chapters and the novel only has 16 chapters - Looking at you The Lazy King... Great novel.) The earliest I've dropped a novel is 12 chapters, and that was only one novel. Others I've read at least to 30-40 before dropping. But those have always been because I personally didn't enjoy the route the story was taking and had nothing to do with the quality of the story. So I don't leave negative reviews since its purely a subjective reason for me stopping to read, and probably not that useful to others.
And when it comes to poor grammar... It doesn't really bother me. I notice it, but I've read so many translated novels that have awful grammar that I've given up caring about it. I just correct the grammar to myself and move on. If they want people to report bad grammar so they can fix it, I will sometimes attempt to make note of it and leave it as a comment so that it can be fixed for others.