I use a five star rating system, but I also use half stars when I feel it is necessary.
guidelines below are a little vague, because there are so many reasons I
can like or dislike a book. That's why I like to do reviews so I can
get into more detail.
Additionally, I don't rate books I don't finish.
To me, it isn't fair to give a rating when I haven't read the whole
story. If I do read more than half I'll try to do a review to explain
why I didn't finish the book.
1 Star: Hated the book, barely finished, wouldn't recommend.
2 Stars: Not my style, didn't like, probably wouldn't recommend.
3 Stars: OK, enjoyable, recommend with reservation, probably wouldn't re-read.
4 Stars: Enjoyed, would recommend, might re-read, but I could put it down.
5 Stars: Favorite, un-put-downable, forcing it on people I loved it so much.
*At this point I have never given 1 Star to a book and 3 or 4 stars are my most common ratings.