The Scarlet Letter
I know, you already read it. I, on the other hand, was a typical teen of the 80's who was more interested in girls and sports than anything else. It was not until my twenties that my English teacher of a sister talked me into reading Stephen King, Stephen King soon turned to Dean Koontz, and Dean Koontz soon turned to anything I could get my hands on. By my thirties I was regularly reading a book a week. Yet, through it all, I never turned to the classics until my forties.
I have read hundreds of good books over the years, but The Scarlet Letter is the best. The reason for this is a personal one; the character of Arthur Dimmesdale deeply resonated with me and transformed the book from simply a good read to an intense personal journey of discovery.
Which leads me to the main point I would like to make. Only you can decide what the greatest book is because it must speak you alone in a special way. Books, like poetry and art, must speak to your own soul in order for it to be great. My favorite painting is Nighthawks by Edward Hopper because it speaks to my soul, yet you may not like it at all. My favorite poem is Annabel Lee by Edger Allan Poe, because it speaks to my soul, yet it may mean nothing to you.
That is what makes literature so wonderful; it has to be personal and meaningful to the reader and, if it is, it is great to you...and that is all that matters.