It really depends on the story. I know some short stories (under 10 episodes) that really dragged, and I know some super long stories (over 80 episodes) that are engaging and leave you wanting MORE. Two of my favorite stories on the whole app are 90+ episodes long (One in classic, hopefully being rewritten in LL @GenevieveM 
, and one in Ink, currently being rewritten in LL @J.Miley ).
I equate the longer (engaging) stories to reading a long novel, for example, Lord of the Rings. It just takes that long to tell the story, but it is OH SO WORTH IT!
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