What Makes a Great Book?

Reading slumps come from kind of reading burn out, where people are trying to tick off these massive, long book bucket lists. Do you think reading should always be a serious activity? Is it really necessary to read great works all the time? Or is it ok to enjoy feel good, popular literature? And what defines a great work? That's a great question. I well, i've not been in the slump for a while because i'm just reading too many damn good books.