There are three definitions competing here:
Good = any given reader's opinion of the work. This will vary across the entire spectrum for any given book. For example my first book currently has 14 five star reviews, and 5 one star reviews. So for some the book was "good" for others it was not.
Good = Lots of people bought the book. The Christian Bible is the best selling book of all time, but it is probably fairly low down on the "people have actually read the book" list. This is true of many of the "best sellers" out there. They are called "good" because the market as determined them be highly sellable.
Good = Some scholars and other erudites have labeled it good. This is most of your classics like Moby Dick, Shakespeare, and so on. I would guess most people have never read them, and they are often free to acquire, but have achieved "good" status because someone that people think should know, said they were.
Frankly, I only care about the first definition.
