As one of the guys over at Holistic Gaming pointed out in an essay many years ago, what we have in games is not really an artificial intelligence; that would be far more complex.
What we have is not an AI, but an AO, or artificial opponent
Now, that said, the best ones I have ever seen have been in the form of bots in various FPS games.
The old Reaper Bot for Q1 wasn't at all bad, and the stock bots that shipped with Quake 3 were better. Furthermore, those stock Q3 bots could be easily modded to be even better, smarter, and nastier than the stock versions thereof.
Of course, tactical decision making is probably an order of magnitude more simplistic than strategic planning.
Oh, and I don't care how much anybody praised the "AI" in Half-Life II, those mobs sucked in comparison to the efforts from id software
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