I was most surprised by the A.I. in STALKER Call of Pripyat.
Once I was to invade a building with many mercs in it.
I came stealthy until I reached a door on that building,and I threw a grenade through that door which alarmed them.
I moved back and went to cover behind a rock,having my weapon zoomed to that door waiting for them to come out one by one,as most enemies do in most shooters.
Only one came out and I killed him.
As I waited for the others,they wouldn't come and I said "WTF ? Are they pussies ? All of them afraid of just me ?"
But guess what ?
They understood my trick,and they went out of the building from other doors,and while I was sniping to the door waiting for them they went all the way around and flanked me,and then I started being hit.
I said "WTF?" again.
I zoomed out and I saw them having me flanked and they where shooting me from so many angles!

They came out from other doors,and they waited until they are many so everybody started shooting me at the same time instead of having to fight them one by one as I do in most other fpss.
Once I was to invade a building with many mercs in it.
I came stealthy until I reached a door on that building,and I threw a grenade through that door which alarmed them.
I moved back and went to cover behind a rock,having my weapon zoomed to that door waiting for them to come out one by one,as most enemies do in most shooters.
Only one came out and I killed him.
As I waited for the others,they wouldn't come and I said "WTF ? Are they pussies ? All of them afraid of just me ?"
But guess what ?
They understood my trick,and they went out of the building from other doors,and while I was sniping to the door waiting for them they went all the way around and flanked me,and then I started being hit.
I said "WTF?" again.
I zoomed out and I saw them having me flanked and they where shooting me from so many angles!
They came out from other doors,and they waited until they are many so everybody started shooting me at the same time instead of having to fight them one by one as I do in most other fpss.