My review rankings are informally based on my thoughts regarding when or how I would suggest getting your hands on the book, which is based entirely on how I think about books for my personal library.
If I loved the book... I'll probably tell you to go get it now, buy it in hardback, etc
If I liked it... I'll suggest that you to wait for paperback
If it was worth reading, but nothing fabulous... I'll tell you to get it from the library, borrow it from a friend, or check out a used bookstore
If I didn't like it... well, that seems pretty self explanatory, right?