the enemy AI in battlefield 3 was as dick
they seemed to be able to suck the intelligence from your own AI allies and make they completely inaccurate, making it take 20 mins and thousands of rounds of ammo just to take out one bad guy in a bare narrow corridor.
Add to that their uncanny ability to teleport from 18 feet in front of you, to right in your face, stabbing you in the chest and then teleporting right back.