I'm getting somewhat okay at Doom and Quake, but somehow I just cannot do well in FPS games like Wolfenstein: The New Order and Half-Life 2. These games that focus heavily on hitscan weapons and enemies.
Games like HL2 actually tend to be easier for me overall. You just have to try to stay away from the enemy line of sight as much as possible. I mean, you obviously have to get out from cover to shoot them, but you get the point.