My rating structure is simple - don't have one. I scratched my brain over that for awhile. I thought about having leafs or tree branches with an increasing number of leaves and other cutesy ideas and decided in the end that people can take what they want from what I say or don't say. Combine my thoughts with those of other reviewers and you should end up with a pretty good idea of whether or not you are going to enjoy the book in question.
I've reviewed some books that I really, really, enjoyed and others that were simply a fun, easy read and I think I make that obvious. So far I haven't read and reviewed a book that I absolutely hated, but if I do, it should be equally obvious.