What Makes A Book Good?

I tend to reread books because I'm a speed reader and as a child I would often finish books so quickly that my mother would threaten not to buy me any more, as it was seemingly a waste of her money. To appease her, I started re-reading the books.

To this day, that's how I justify buying a book in hardcover. Will I re-read it?

So my rating system is simple, especially when comparing apples to oranges (i.e. YA to Historical Fiction to Chick-lit):

Did I enjoy it enough to re-read it?

If it's below a 4, probably not.