Stories of such magnitude that they can only be described as 'Epics' These chapterific, word-count busting tomes of might show world-building, character growth, multiple threads, huge casts or involved plotlines.
Asking the hard questions, and wondering about the very fabric of reality itself. These stories focus on the characters, or the world in which they live and ask why it is, or what it ought to be.
Not everything is fun. Sometimes the truth hurts, and the hard facts need facing in the cold light of dawn. Alternatively it may be funny, but it's black humour at best.
All the frivolous and silly stuff that makes you feel like bouncing as high as a kite; or those nice stories that give you the warm fuzzie wuzzies. These will give you a real boost.