I use a 5 star rating system that is both simple and subjective. There is no formula for getting a 5 star review on my blog, and no clear list of attributes each 5 star book has, because reviews ARE subjective by nature.
Where you’ll find consistency and specific literary attributes I look for is in the text of the reviews themselves. I always give a detailed account of what drew me to the book in the first place, what my experience reading it was like, and why I gave it the rating I chose.
★ ★ ★ ★ ★ = Your book is awesome! I loved it! How did I not know about it before this?
★ ★ ★ ★ = I really enjoyed the book; it was a good solid read.
★ ★ ★ = I liked it, but there were some issues with it.
★ ★ = I didn’t like it, because I found a lot of issues with it.
★ = I really, really disliked your book.