★★★★★ - I absolutely loved this book.
★★★★☆ - I really, really liked this book. There were some flaws that kept it from being a five star book, but I would still definitely recommend it.
★★★☆☆ - It wasn't amazing, but it wasn't necessarily bad, either. I liked it.
★★☆☆☆ - I didn't like this book very much, but there were some things that kept me from hating it. Overall, it was okay.
★☆☆☆☆ - I really, really didn't like/hated this book. There were too many problems I had with it, and the bad outweighed the good immensely, if there was any good to begin with. Most DNFs of mine will be given one star, unless it's a book like The Passage by Justin Cronin, where the first half was excellent beyond belief, but the second half was lackluster.
If I give a half star rating (let's say 4.5 stars), that means it had some qualities of a five star rating, and some qualities of a four star rating. The same applies to the other half star ratings I would give, such as 3.5 stars, 2.5 stars and 1.5 stars. Books I give five stars to are books I love with a burning passion, books I give 4.5 stars to are books I love, and books I give four stars to are books I either love, or really, really liked, depending on the book.