It really is surpising how little AI has evolved over the years, especially in shooters. While graphical advancement is an ever-continuing process, one could say the benchmark for combat AI stems from 2005, when the first FEAR was released. After that title, games only sporadically displayed AI that didn't seem completely retarded in comparison, Killzone and Crysis being examples of that (although the AI in the latter still had many flaws). One game that displayed fantastic AI was STALKER: Call of Pripyat. Not only the combat AI was exciting, but also the behaviour of NPCs, who engaged in the same activities as the player in such a convincing manner that it was near lifelike (bar the crappy animations). It was also non-scripted, which is a huge pro over games like CoD, which rely too much on set pieces.