1 - Awful: There are severe flaws in both story and writing style. I hated it so much, I wanted to gouge my eyes out while reading it. (Thankfully, there are very few books this terrible.)
2 - Flawed: While there may be creative or enjoyable moments, plot holes and other deficiencies are present. For a variety of reasons, the book is clearly not as good as it should have been.
3 - Enjoyable: This book is enjoyable to read and for the most part, was well written.
4 - Stellar: This book stands out as being well written and a real page turner. The story grips you, making it hard to put it down.
5 - Seemingly Perfect: The story and execution are of the highest quality. It is unclear to me how the writer could have done better. (These books are also exceedingly rare.)