I thought about this before, but what is rating in books? It seems that it is rather up to preference. Is there anything that you would like to change about access? Is there any argument about the matter?
My rating system goes from two thumbs up to two thumbs down, which is essentially 5 stars. And it is, of course subjective to me.
If I was grading a contest, there are usually other criteria, such as character, plot, setting... as compared to the other entries.
I think you start to get in trouble if enough people start to come to similar conclusions as to quality and value of the writing. Too many 1 star reviews by enough people, then its probably a dude. (Unless its a political thing, cause then its only fans and haters).
It is a subtle business. There are so many areas to look at besides the dismally crude star system. Reviews? Fine if it is a reviewer you respect- Michael Dirda at the Washington Post comes to mind. Or Publisher's Weekly. Here's a fairly subjective system of my own: Take a book you really loved and see what reviewers have said about it. After reading it, mind, no peeking at the end flap. Some good reviews are the kiss of death, for example the National Inquirer (US) or the Sun (Uk).
Also, beware of books only touted by other authors. There's a base reciprocity system at work there, sad to say.
Also, the Water Pill. As someone all too familiar with that particular medication I think it would be the height of opprobrium to piss all over a book you didn't like.