Man of Honour
The bit in FEAR with the guys who're "hard to see" really had me on my toes but I have to say SS2 is the scariest game i've played ever. Still remember playing that whilst back in uni... It was xmas and being the miserable sod I am, I didn't go home until way after everyone else... I took a break at 4am to go to the bathroom. Probably the most scary trip to the bathroom in my life