Source : Webster's Revised Unabridged Dictionary (1913)

Interestingness \In"ter*est*ing*ness\, n.
   The condition or quality of being interesting. --A. Smith.

Source : WordNet®

interestingness
     n : the power of attracting or holding one's interest (because
         it is unusual or exciting etc.); "they said nothing of
         great interest"; "primary colors can add interest to a
         room" [syn: {interest}] [ant: {uninterestingness}]