It is a parody of retro games and pop culture as well as the popular Grand Theft Auto series. The game's title is a reference to River City Ransom, a 1989 sandbox brawler reminiscent of Grand Theft Auto.
In Retro City Rampage, players take control of a henchman of a major crime syndicate known as the Jester. The game is inspired by Rockstar's Grand Theft Auto games, in that the player can complete a variety of missions within an enormous city that is open to explore. There will be around 50 story missions and 30 challenge levels in total.
Source: Wikipedia, "Retro City Rampage", available under the CC-BY-SA License.