I just realized the difference. Or, so as not to be grandiose in my expounding, maybe not so much between a good book and a great book, because what do I know about such stuff. But the difference between a good reading experience and a great reading experience. Subjectively. Speaking for myself only. Here it is.
If I'm in the midst of a great read, I can barely think about anything else. I wake up dying to get back to the book. All through the day's work it lurks behind the nonsense toward which I'm forced to direct my mind. Most of all, I dread the ending. I want to never stop reading this wonderful book. I wish I could keep turning its magical pages forever.
If the read is merely good, my mind starts wandering a bit as I move through the second half. As I proceed, I start a running countdown of how many pages are left. Most of all, with the turn of each page, I'm in a rush of impatience to be done with it. I itch to start reading another book. If I have a particular book in mind, if a book I have high hopes for is waiting its turn, the itch turns well-nigh unbearable. I'm in such a state at the moment. I very much like the book I'm reading. But another beckons. I'm late! I'm late! For a very important date!