Well, I think all FPS AI's will have their dumb parts. I keep hearing about Far Cry 2's AI, but when I played it, I thought the AI did a pretty good job of rushing and flanking if they saw or heard me. Of course, I could rush up and knife a couple of them at times, but considering the fact that it takes quite a few bullets to kill I didn't think the AI was too bad.
The AI I absolutely was disgusted at was the people in Condition Zero: Deleted Scenes. It's the single player missions that came along with Counter-Strike: Condition Zero. Your teammates will literally crouch right in front of an enemy and start shooting at him point blank.