The sub-genre of "Open World RPG" is a surprisingly small considering the massive sales of many of these games. Though a number of action-adventure games have open worlds, RPG's, seemingly a perfect fit, mostly rely on Bethesda, and the occasional Borderlands or Witcher game these days. And of these, my favorite would have to be Fallout: New Vegas. It is not just the setting and premise that sells the world, but also the tone. Though "war never changes," this is because humanity never changes, which ends up working for the better in many cases. The DLC in particular relies the theme of humanity's eternal nature, but the core game also is a great depiction of this. It also helps that the gameplay and developing characters feels a bit more diverse and deep than that of Fallout 3, Oblivion, or Skyrim. New Vegas has flaws, but remains the open world RPG I judge others by.