I use the following subjective ratings to classify my fiction consumption. In the perfect world, all my reading would fall into ratings 1, 2 and high 3s.
A "classic", that should be read by everyone.
A good story, well put together, with some definite depth to the plot, characters, or ideas. Definitely re-readable.
A good enjoyable story, worth the time spent reading, but maybe not particularly deep. Some may be re-readable.
I read it, and it was better than nothing, but I won't be doing so again.
I read it, but wouldn't have if I'd known... (It might have been saved from unfinishable only because I read it in a single sitting: if I'd been interrupted, I might not have picked it up again.)
-- Ambrose Bierce
I couldn't finish it because it was so bad, or boring, or whatever. I said the Eight Deadly Words: "I Don't Care What Happens to These People". (I classify more books as unfinishable that might have been just a waste of time a few years ago, as I have less time to read, so tend to be more impatient.)
-- James Nicoll, rec.arts.sf.written, Dec 2000