For those of us who tend to read the same sort of stuff over and over again, I give you Marcel Proust on what makes a good book:

So it is that a well-read man [or woman] will at once begin to yawn with boredom when one speaks to him of a new ‘good book,’ because he imagines a sort of composite of all the good books that he has read, whereas a good book is something special, something unforeseeable, and is made up not of the sum of all previous masterpieces but of something which the most thorough assimilation of every one of them would not enable him to discover, since it exists not in their sum but beyond it.