For AI problems I love what I did in MGS3, I got up to 95% camo and hid in some rough shrubs, as a patrol guard walked past I managed to get a tranquiliser in his neck, those who have played MGS3 know that one dart will take a while to send someone to the land of nod. The wierd thing was, he did become alert that he had been shot in the neck, but after checking around not seeing me he said "Huh? Musta been my imagination." With a projectile syringe still lodged in his jugula.
Also Goldeneye, a classic, but did anyone notice when a soviet pulled off a dramatic combat roll, but while he was at it you thudded into him with about 30 bullets, he would have to finish his combat roll, stand up straight, then acknowledge he had been shot, then fall down.