Follow the thread....
From SimCity to The Sims to this... Spore (official preview site, kinda sucks), a game which starts at the cellular level, literally in the primordial ooze, and lets you evolve your own creatures.
Better yet, they live in a world inhabited by creatures that OTHER players have evolved in their own games. Atlanta-boy-done-good Wil Wright gives an amazing demonstration of the game here (Google video, watch this one!!!), with a longer speech here about procedural content... defining actions instead of objects, as I understand it. (This is exactly how The Sims and The Sims 2 work- the game defines the actions, but the player sets up the environment and the characters which inhabit it.)
As if I wasn't already addicted to all of Wright's sim-creations... this looks so addictive, I'm scared for my job.