Story-wise Scarecrow plans to unleash a chemical weapon on the city, thus most of the civilian population has been evacuated. What's left are an outnumbered police force and hundreds upon hundreds of gang members. Events of the previous games are taken into account, specifically the Joker's death. The character will NOT be back, but his passing has had an impact on the city and the game explores how the villains now fill that power vacuum.
Zubis said: They've flat out stated Joker will not be back in this game. Which is a good thing. https://www.darkhorizons.com/news/31130/more-details-on-batman-arkham-knight?utm_source=twitterfeed&utm_medium=twitter
reido said: I'll believe it when I see it.