Biggest problem i have with the enemy AI is their ability to shoot through fog, they spot you nigh on straight away whether your proned or crouched/behind a rock, when you do manage to sneak up and fire they know with pin point accuracy where you are (even if your using a silenced weapon) and then headshot you lol.
I do like the fact that they seem to flank you and also dont just stand around when they're under fire.