Disclaimer
I am exquisitely aware of my complete lack of qualifications to critique any author's work. However, I aspire to be an active reader, not a passive one, and formulating an opinion about what I read seems like a good place to start.
The purpose of my reviews is merely to help me record, process, and remember what I read (which would otherwise be forgotten immediately, if not sooner). The 5-point rating system is no more than a convenient method of recording my personal opinion of a book's quality and value at the time in which I read it.