This video breaking down the artificial intelligence in Skyrim is one of the clearest explanations of the problems with enemy A.I. I’ve seen. Using Skyrim’s user creation tools as a testing ground, the author tweaks the behaviors of halfwitted mages until they become adaptive, formidable adversaries.
The author narrows it down to exploration and exploitation. Exploration is a good thing, because it compels the player to experiment with new battle tactics without being punished by instant death from cheap enemies. On the other hand, stubborn enemies that can always be exploited with one tactic or attack is a classic sign of bad A.I. (Think: every Zelda boss fight you've ever played.) Unfortunately in most games, “rewards are high for finding an exploit, and punishment high for trying something new,” he says.
He then goes on to redesign some of the most intelligent mages you’ll ever see in Skyrim. Bethesda, hire this guy.