There are plenty of horror video games out there that do a great job of putting the fear of God in you. From Resident Evil to Silent Hill, releases both new and old still have that special concoction of fear and anxiety that makes for the creepiest gaming experiences.
However, sometimes the scariest games are the ones that aren't actually billed as horror titles. Maybe it's because you're more prepared to be shocked in those, already on the defensive and looking out for the game's tricks, whereas in these unassuming titles you're caught well and truly off guard by an unintentionally terrifying moment.
In many cases something which should have been innocuous comes across as pant-wettingly absurd because of dated graphics making everything already look a little surreal, but other times you get the feeling that the devs were trying to make something normal, and the Lynchian part of their brain simply took over with the intent of morphing that into something human eyes should never be subjected to.