Similar to, but not quite as strong as, the term 'Cliffhanger', used in various media such as TV shows to denote a moment of extreme suspense or surprise at a sudden plot development or revelation which occurs at the very end of an episode. A Slope Hanger is the milder version of this. You're not quite on the edge of your seat, but your cheeks are debating it.
"Lost ended on a slope hanger last night; who's that new guy??"
by PjFitz February 25, 2010