Perfect Dark for the N64 is hands down my favorite game of all time. I still play through it every few years to enjoy the campaign and then I play the simulation mode for hours against the bots. I love the bots because Rare coded in some basic personalities for them so that they acted more unique. Like bots that noticed if you killed the worst player over and over would seek you out, the Justice Bot!
I was also impressed by the AI of the bots, very advanced by the standards of that time