So what exactly makes you want to play a game after youve beaten it the first time? There are certain games that you can beat in a one hour sitting (I think it was Yoshis Story or something of that), and then there are games that youll always be playing (easy example: Tetris).
Well, those are the older games, and we're already a few years well into the next-gen gaming. Is it the multiplayer options? That allows you to have a constantly changing opponent, since you cant exactly read them like you would with the built-in AI. Perhaps gameplay? Just something about it thats some different from all the other lackluster games. Or maybe its just the want to be as complete and powerful ingame as you can?
There was another big item in addition to multiplayer that I really wanted to add, but its slipped my mind.
What are your thoughts on this? With the rush of sequels out, it seems that theyre currently running dry on ideas, so there would be some logic in keeping the players happy on select games.
EDIT: Just remembered, and it was so obvious, on this site too!
Ahem. In addition to multiplayer, could it be the mods? Having the ability to be able to change some aspects of the games so that while youre playing the same game, it has the feels and style of something different. Example: Half Life and Counterstrike. The mod on HL was so popular itself that they eventually used it to produce its own product, and led its way to its own sequel.