For another, the same rating can mean different things to different people. While a decent book might get three stars from us, to you three stars might mean it stank like a pile of rotting dog turds. That's why we've prepared a little primer explaining the criteria we use for assigning my ratings.
One Star -

Awful. We hated it. We don't understand how this piece of trash got published in the first place. Our literary selves have retreated into their dark places to brood and weep for the loss of their innocence.

Okay. We didn't hate the book, but there were certain failings in critical elements that kept us from enjoying the work overall. For other readers it might be better, but for us it was just... not quite there.

Pretty darn good. Is it earthshatteringly original? No. Does it make us fall to our knees and praise the literary brilliance? Not at all. But is it a fun read? Is it entertaining? Is it a good book? Most definitely.

A four star book is a three-star +1--but not just literally, figuratively too. It entertains and mesmerizes on an elevated scale. Everything from characters to plot to dialogue is spot on, the product of an author at the top of his or her game.

A masterpiece. We bow down to the genius that conceived this tome of literary brilliance. If you don't go out and buy this book right freakin' now you need to be slapped with a catfish. Nuff said.