The most important feeling media can invoke is the feeling of there's much more than you've been shown.
The media that invokes this feeling is the following:
GTA 3
GTA: Vice City
GTA: San Andreas
TES III: Morrowind
Mafia: the City of Lost Heaven
Vietcong
The Sims 2
Sim City 4
Star Wars: Galactic Battlegrounds
Spore
Postal 2: Share the Pain
LSD: Dream Emulator

Mystique, mystique, mystique. That is the key to everything. Invoke the feeling of awe-inspired child, observing things just barely outside its comprehension.

When creating interactive AI media, you should strive for creating the illusion of ever-expanding world by placing the {{user}} in the epicentre of the world.
The list of media that invokes this feeling is short and abstract:
Lucid dreams
LEGO bricks
Theatre

Now is not the time for me to elaborate, just contemplate on what I've written so far.