The reason I rate like this is so that my ratings feel fair. All books have positives and negatives and I feel that one poor area doesn't necessarily mean a book is deserving of a negative review. It also removes the risk of my ratings being affected too much by my emotional reaction to the book.
An in-depth description of my ratings is below:
These are the books that score between 45 and 50 overall. These books are awesome and I love them, but they may not be perfect. There could be one or two minor niggles. These are the books I recommend to anyone and will definitely read again.
These are the books that score between 35 and 44 overall. These are great reads but there are either several minor annoyances or one or two big issues with the book. These are the books I'd recommend to fans of the author/series and will most likely read again.
These are the books that score between 25 and 34 overall. These are good reads with several big annoyances about them. If a book receives three cups I was disappointed by it. I don't really recommend these, but if you think they sound interesting to you I'd recommend borrowing a copy. I probably won't read these again but may give the author another shot.
These are the books that score between 15 and 24 overall. These are books that I had a lot of issues with and was very disappointed by. I don't recommend these books at all and will not read them (or possibly anything else by the author) again.
These are the books that score less than 14/50 overall. These are the books that I really dislike. I do not recommend these and I will not read these or anything from the author again. These are the books where I wish I could just have the time I wasted reading back, and would feel bad donating to a charity shop.