Tizzysawr: I have, twice, as university projects. First one was a Reversi game where I didn't code a thing, but was in charge of the looks of the game (all pre-rendered in Maya). It was simple, but it looked amazing :P
Second, a pseudo sim city. It ended up being pretty basic, what with being a school project, but it took huge amounts of work. It wasn't too entertaining, but simulating all we did (plus the game played itself) was pretty hard. Made me respect simulators quite a bit more :P
Yeah, it's really easy for a simulator to go out of control fast. I learned that doing neural nets, it was really hard to code one that didn't get epilepsy (all nodes firing all the time).