Prohibition

20th century American history has been popping up everywhere lately, in film, television and games—Mad Men is insanely good, L.A. Noire was in many ways a triumph, Black Ops covered the Cold War, etc. HBO's Boardwalk Empire has proved that the prohibition era in the 1920s was surprisingly exciting, considering no one was supposed to be drinking for well over a decade.

It was the golden age of gangsters, and even a historically accurate game could feature plenty of shootouts, smuggling runs, kidnappings, political intrigue, and all the other makings of a compelling game.

Plus, everyone loves to run around games like Bioshock, Deus Ex: Human Revolution and Mass Effect downing booze as the screen gets blurry for ten seconds to simulate the effects of being wasted; why not make a whole game about it?