A scale of one to ten is nice, and all, but it has little meaning when you see people bag on a book, but give it a seven. So, here's my scale and some questions and answers about how a book might be placed.
I do include a little note with my verdict most times to indicate to you why I rate the way I rate.
10 -- The Comfort/Awesome Book. I love this book wholeheartedly. I probably don't like you if you don't like this book. I think it says something about you. Not only do I love the book, I probably re-read it annually. Maybe more often. When I'm feeling down, I pull it out. When I'm feeling tired, I read it. I read it because I can. Very few books attain this level of perfection for me. The Hero and The Crown by Robin McKinley. The Blue Castle by L. M. Montgomery.
9 -- The I Love This Book. A really great book. I recommend without reservation to anyone I think has even minor overlapping tastes with me. Alternatively, a book that I read when young which has great meaning to me, but might actually be lesser ranked when not viewed through the lens of a loving childhood of reading books.
8 -- The Hey, That Was Really Good Book. This is the book which I think about for a while. I remember passages and go to reread those passages for no reason other than because I can. I might pull the book down and read it when I've got no other new books.
7 -- The I Want To Read More Book. Once a book hits the score of seven for me, it becomes a keeper. I want to add it to my bookshelves. I look for the author more often. I keep an eye out for sequels. I might not love the book, but I enjoyed the majority of it.
6 -- The Possibility Book. I liked the book, but it didn't really ring any bells for me. It's kind of the "I wouldn't kick it out of bed" of books. I'd probably recommend it to people depending on their interests. This can be a book where the story was eh, but the concept was fantastic, or one in which I mostly didn't care that much for the whole of it, but I couldn't help but enjoy some parts of it so much that they made me enthusiastic.
5 -- The Eh Book. Neither good nor bad. Most likely if I've given this score to a book, it is because I got through the book and most of what I had to say about it is, "Well, that was a book. It sure was." The characters neither excite nor anger me. The story is so-so. A lot of fantasy novels and even more mystery novels I've read fall under this heading.
4 -- The Forgettable Bad Book. A book that is only minorly awful. Most likely, it's entirely forgettable or filled with weakly drawn characters and unlikely or silly situations and conflicts. Alternatively, it might be a badly written novel with an interesting concept.
3 -- The No Good Book. While not offensively bad, I probably spent the majority of the book rolling my eyes and wanting to throttle the characters. I can come up with little good about the book when reviewing it, but, luckily, I'll probably forget the majority of the book about a few weeks after finishing it.
2 -- The SO BAD Book. A bad book, one that I also probably threw out, but not as grotesquely offensive as a book I gave a one to. "Just" offensive enough that I hate the book and characters (and myself for finishing it), not so offensive that I come away hating humanity and the author after reading. Many a series romance novel for me ranked a two. Why do I keep reading them?
1 -- The Ugh Book. I can't even use words to discuss this book I hated it so much. This book was so bad that I wished I could have set it on fire. I possibly threw it at something prior to throwing it out so that no one would ever possibly finish that book again. I can't actually come up with a good literary example, but Sin City is a good representative of the 1 category for me for movies. I felt like throwing up when I watched that in theatres.
DNF -- Clearly a "did not finish". I might not have finished because I got bored. I might not have finished because it was hideous. I might not have finished because the book and I were just not a nice match.
Now, some Q & A.
Q: How would you rate a book that was mostly good but forgettable?
A: Probably a six, maybe a seven. It really depends on how much I enjoyed it at the moment I read it and how I feel about it about a month after the fact.
Q: How would you rate something like the Grapes of Wrath, which you hated but which was well-written.
A: Mostly likely a four or five. While I got no personal enjoyment from the novel, I realize there was value to it. If I found such a work especially offensive, I might go as low as a two or three.
Q: How would you rate something like The Belgariad by Eddings, which you read when you were young and impressionable and enjoyed silly epic fantasies, but which you realize now IS silly.
A: I think I'd go as high as a six for the series, and seven for some individual books. I realize it's not quality, but when reading them, I can't help but view them through a lens tinted with love for the way I felt when I first read them.
Q: How about something you felt was a great, but where you feel the author is a giant tool?
A: You mean like Ender's Game? Yeah, I'd rank that based solely on how I feel about the book, but I couldn't promise that my view of the author wouldn't color my view of the book. A truly enjoyable book such as Ender's Game can breakaway from my dislike of Card, but Xenocide definitely cannot.
Q: How about something like Twilight, where you it is almost offensively bad, but it goes back to being funny in parts because it is so bad.
A: How can I give vampire baseball games anything less than a four? I mean, objectively, I think it is worse than that, but I laughed about that vampire baseball scene for like a day. That could be my favorite sport ever.