If you look through my reviews, you'll see that most books earned either four or five stars. That isn't because I'm lenient on authors, it's because I'm very selective about what books I accept. Below, I explain my ratings.
5 Stars: Excellent. There were no or very few errors in the text. If there were more than a few errors, they were very minor and uncomplicated or easily overlooked. (See Term 2 of my review policy.) There might have been two or three minor aspects of the story that I thought could have been better, but I'm on the bench about whether I would truly want them changed or not. I adored the story and highly recommend it.
4 stars: Great. There may have been more than a few errors, but they mostly didn't throw me off track. And/or there were some minor aspects of the story that could've been improved. I still loved the story and recommend it.
3 stars: Good. There might have been some errors that threw me off track, but they weren't so bad as to ruin the story for me. And/or there were some aspects of the story that could've been better, but it was still enjoyable. It has a lot of potential and is recommendable, it just needs some work.
2 stars: Okay. There were many errors and I had a hard time focusing on the story because of them. The characters or other story elements may not have grabbed my attention, but there was still some aspect I found worthy of my time. I might have considered not completing the assignment. Needs work.
1 star: Bad. There were many highly disruptive errors. The characters or other story elements didn't get it for me. There may have been something that kept me reading, but I lost hope that the story would get better at some point. I strongly considered not completing the assignment and finished the entire work under physical pain.