The Importance of Density in Games

In a game, if there's not enough in the space, it's so disappointing. I really crave density in games that I play. We've actually been playing oblivion, which is not obviously post-apocalyptic. Any room you go in feels like a full world. Upside of the apocalypse will get to be a bunch of creeps. That's awesome. What are other examples of this in games? I want to know more.