If the story makes sense to me, then I have a good start. If I don't get destracted by issues in regards to structure or grammer.
If they have a clear comprehension of the story. They are engage and invested in the actions and story of the main characeters. They want to visit everypage on the website.
If the user posts positive feedback on a social media site. If there posting helps bring new viewers to the site.
Even more positive social media feedback. Written reviews on review sites. A new load of first time viewers visiting the site.