Ratings system? Here it is:
5 stars: This will change your life. Stop whatever you're doing and read it.
4 stars: Pretty darn entertaining, but not life-changing. An E ticket ride.
3 stars: Well, I finished it. And maybe enjoyed part of it.
2 stars: Really? This got published? Yuck. And maybe I didn't finish it.
1 star: Truly insipid and vacuous.
(1 and 2 are rarely seen, because I don't think its fair to rate what you haven't finished, and life is too short to finish that rotten sort of book.)