While 5-star system underpins most ratings benchmarks used worldwide, I draw inspiration from Roger Ebert's 4-star system. Though not related, Ebert's system has definitely spurred my own ratings rationale. Unlike Ebert, I have a clear label against each category, defined as follows:
Unputdownable - 4 glowing bulbs indicate that the book is a must-read. Unless you are being paid to watch TV or surf internet, you must make time to read this book. Think of it like you visit the Louvre and walk straight past the original Monalisa. This category of books stays with me long after I have read them. I often feel an unyielding itch to re-read them, primarily because of their superior, insightful content and masterful authorship. A few noteworthy examples are 'Thinking, fast and slow', 'Antifragile' and 'The Black Swan'. Nothing else satisfies my intellectual cravings as these books do.
Recommended - High on interest and intelligence quotient, I commit three glowing bulbs to books that are mentally stimulating and intellectually satisfying. That said, the subject matter might not be unique, and there could be a few loose ends, too. Nevertheless, the books' positives far outweigh the shortcomings.
Average - These books are one time reads. While I like some parts, there are parts that put me to sleep. Author's lack of clarity and control on the subject doesn't help either.
Lifeless - 1 glowing bulb means that I had to trudge through the book. Books with this rating are irrelevant and avoidable. Baffling subject matter, stodgy pace, flawed facts and at times, disinterested author(s) - all are the hallmarks of this category.