I tend to think of it as an Elseworlds because of the characters. Joker, Oswald, Crock, and others are much more "street-level" here, concerned with regular crimes and rackets that are normally dealt with by normal gangsters and thugs in the DCU. One could argue that this GN just shows an off-day (or a mostly Batman-less one). Most out of step is Harley, who is completely unlike the Harley we regularly see. There's also the matter of Joker's glasgow smile.