Just to give you an idea, Creatures faithfully simulates real-life biology down to the genetic level, with sophisticated biochemistry and neural network brains. What this translates to is that they are constantly evolving lifeforms that are capable of learning and reacting to their environment. They'll remember their past experiences, so if you were to slap them for eating a poisonous fruit, they'll associate the slap with that action and adapt accordingly in the future. When the creatures breed, they pass down their genes to their offspring, and mutations and changes in their patterns of behavior can and do occur generations down the road.
You play more or less a god-like role, and you can choose to participate as little or as much as you want in their development. You can selectively breed different species to see what sorts of interesting results you can get in their offspring. Or you can be like me and play the role of mad scientist, subjecting them to trial-based tests to ensure that the strong prevail and only the survival-linked genes are passed down. As for those who don't make it, I systematically destroy; either dropping them into the piranha pond or blowing them out of the airlock, depending on my mood. You can call me sadistic, but the point is that the game is set up in a way to make any of this possible.
As far as I know, it's about as close as a game has gotten to simulating actual artificial intelligence/life. I picked up Exodus on a whim a few months ago because the idea behind it was so intriguing, and I enjoyed it a lot more than I thought I would. Just be sure to have the right mindset and know what you're getting into.
Post edited May 08, 2010 by Spritescaper