Red has a point though. I got that feeling while working on Drop Fighter. After weeks of working on making the movement of the player's fighter feel right, and getting the landscape in, I added enemies. And then there was a long process of tuning their AI.
And then, finally, they began attacking me pretty well. In one game, I decided to see hw well they chased me, so I hit the engines and flew away from my command cruiser.
I looked behind me, and, to my surprise, they made only a token effort to chase me before turning around and starting to blast my command cruiser.
I hadn't expected that, although it was a perfectly normal side-effect of the way the AI was written.
At that point, I realised the game was COMING TO LIFE!
And then, finally, they began attacking me pretty well. In one game, I decided to see hw well they chased me, so I hit the engines and flew away from my command cruiser.
I looked behind me, and, to my surprise, they made only a token effort to chase me before turning around and starting to blast my command cruiser.
I hadn't expected that, although it was a perfectly normal side-effect of the way the AI was written.
At that point, I realised the game was COMING TO LIFE!
I know exactly what you mean. I agree that AI is one of the main things that causes this, since it's usually unpredictable, and it's fun to watch your game's characters "take on a life of they're own". :) I've have this "feeling" mostly when my major projects near completion (like with BattleTanks II).