In Starcraft & Warcraft, the AI does not have unlimited resources and you can defeat him by going fullscale offensive attack against him. The thing that differs a human from AI in RTS is that the AI controlls everything indually and instantly. If it wanted, it could probably make a movie starring itself as the main villian, the main hero and the civilian cannon fodders. But the AI in Warcraft 3 was horrible. Not because it was bad, but because it aimed to get an hero right away. The heroes are a fun addition, but for RTS, they really aren't... They ruined it really since like one hero can kill an whole army <_<
Star Wars Battlefront 2 has hilarius AI. I always play that game in hardest difficulty and it isn't harder then playing Easy really. Things really get fun when you play "Hunt" and end up on Endor planet with all the Ewoks since the Scout Troopers aim is like dropping a tomato to the ground and MISS it! They litterary throw granades all over the place, blowing themselves and each other up all the time.
AvP 1 have one of my favorite AI. Surely it isn't smart (marines panic almost instnatly and almost always) but it's an explorer type. It will litterary explore the whole level to find you. For example, my favorite level is the bonus level which was also the demo level "Invasion" which exists for all 3 races. But the fun part is to play it as an Alien, then cheat so you throw out like 50-100 Alien, Predalien, Preatorian bots. You just smack them all out into the ventshaft there at the start. Then you go to the Predator start area on the level and spawn a Predator bot. Then you throw out some more Marines at spots with tougher weapons and such. Then you wait (god mode of course) for like 5min before walking slowy over the whole level and seeing how it has gone for them. The aliens will most likely have killed of the majority of humans (and many of themselves since they like to hug Sentry guns and jump into fans), the humans will walk around, panic from time to time and shoot at stuff. The Predator however, may have walked all the way from where you put him out, to the top of the level, and down again, hunting everything on the level. I opened up a door at the top (auto-open) and as they opened, the Predator was butching two Aliens with his spear, poked ones head of, then sliced the other in half then wrist-bladed an attacking Predalien to death, then he charged me <_<
Appart from that, the AI in AvP1 really scares me sometimes.. Quiet often actually. Some Aliens scream constantly, but some will sneak up behind you and bite you which usually makes you jump your chair, turn around, and die from his bitchslap as they do sometimes, or his tail, or another bite. Munch..
When speaking of Redicilus IMBA AI, I'm suprised no one has brought up Shao Kahn on the hardest Difficulty or Noob Saibot or any of the Mortal Kombat games because they were just redicilus. They charged you instantly and bam, you were dead.
And also, the Original Rainbow Six.
You look into a room and someone from the other side shots a clear headshot right through your nose from 900 yards perfect aim NATURALLY like THE Yathzee would say. And this is how your whole TEAM died because he shot them INSTANTLY.