Spore

Ran and Greif already linked to this, but I have to add my own recomendation: if you think computer games are cool (which I do, in the abstract, I don’t actually play them myself sort of way), you should watch Will Wright’s demo of Spore, a game in development that has been described as from bacteria to galactic god.
There are a lot of cool things to say about this, but I think the main thrust is the shift from player as consumer of canned media (the CD-ROM view of reality) to player as creator and storyteller. Also, and I think this is sort-of cool, the game uses networking in an interesting way: instead of players beating on each other’s characters, anything they design gets uploaded to a server and used by the game to generate challenges for other players (or offer them cool toys).
Long ago, when I was scriptwriting for Neora’s CD-ROM/Internet game, I thought of something vaguely like this: to design a game for a slow network, you should have something smart to send over it, like a corewar bot the player can design or something. But that idea is like a bacteria to this galactic god game.