The most interesting mob's AI I,ve saw in Dungeons&Dragons Online. DDO intelligent mobs are choosing their target depending of current situation, regardless of any past player's actions. Of cource, some dumb mobs like slimes just slam to a nearest target, but other mobs, who must act intelligently, do it. Mobs like kobolds or orcs act more likely to an offline game. They are attacking low-armored mages before they cast their powerful magic. They are focusing on a low-health PC to take them out, regardless of aggro generated by that PC. The casters and shooters are running away from fight looking for a proper position on a high place or something like it, or they just running to a nearest ally for reinforcement.
I'll be happy to see really intelligent mobs in V13. Excuse my bad English... I am a Russian bear, it's hard to type with claws.