Sacrificing Deus Ex to the gods...

[Zarathustra]

You can turn off the highlighting, aiming reticule, or waypoint markers in any difficulty. I prefer the hardest difficulty with the aiming reticule turned back on. The game already penalizes you for blind firing without having to make things even harder in that regard.

As for shooting enemies in the face, if you're VERY quick, you can line up your shot, pop out of cover, and down them before they have time to react. There are some quality QuickDraw moments in the game that can mix things up.