Doorways & walls edges - they really need to have a cover point on the left an right side of each door. Some doors have this others do not and the inconstancy is a killer. Another issue is the AI can shoot through them. I find myself where bullets are coming straight through the walls and hitting me even though i can't even see the enemy since it is on the other side.
Camera Angles -- in development we were promised to be able to set the camera angle any way we wanted or at least from a few presets. For instance right now the camera is hiht up and looks just slightly forward so the AI can see you long before you can see them. I would like to have the camera lower down closer to the back of your character and so you can see forward like 3rd person almost.
Either the above of have NPC AI use the same logic as you do for acquiring a target so if they are behind a wall they can't just shoot you and would have to walk around or wait for you to enter their room.