When I have finished I book and I am thinking about a rating, this is what I base it on:
Feeling: Does the story give me the feels? Does it have that je-ne-sais quoi?
Writing: Is the story well written? Is the writing poetic and detailed, or sloppy and haphazard? Am I constantly taking down quotations that I don’t want to forget?
Plot: Is it engrossing, or am I bored? Is it logical and ordered, or confusing and messy?
Characters: Are they fleshed out? Are they likeable and relatable? They don’t have to be nice – I can like and relate to the most awful characters. How are the female characters represented? Is the cast diverse in race and sexuality?
Themes: Does the story have an overarching theme or moral? Did I learn something about the world or myself?
Cover Design: Although I don’t really factor this into my book rating, I like to comment on the design of the book cover.
How I rate:
5-stars: Damn near perfect. I loved it!
3-stars: I liked it, but it didn’t blow me away.
2-stars: It was ok, it is recommended with reservations.
1-star: It was a complete waste of time; I do not recommend this book.
Finally, I tend to rate books based on what they are, and whether they meet my expectations of that. Is the book a light, fluffy read? Is it supposed to have in-depth world building? In general, I consider a story successful if it took me away from the real world.