When going about my day-to-day business, I like to maintain a healthy level of heart-rate-skyrocketing paranoia. So naturally, I find myself glancing over my shoulder a fair bit when I'm out and about, and it's quiet - too quiet. Slender, I think, is a pretty good validation of all my greatest fears. It's based on Something Awful's Slender Man myth (which I confess to having known nothing about until now), but ends up feeling a bit like Amnesia - dread-inducing use of complete darkness and all - but in an open forest with one hyper-spooky thing constantly Right Behind You.
For the most part, it works well, too. My first couple minutes were a bit aimless, but after I started stumbling across panic-stricken scrawlings about the Slender Man's delightful hobbies (leisurely strolls through nightmare forests, leisurely strolls through nightmares, stealing souls, etc), things began to pick up. I didn't actually see him until about ten minutes in, but that made it all the creepier. He was just standing off in the distance, staring straight back at me. But the game makes it abundantly clear that staring back for more than a few seconds will kill you, so I immediately took off sprinting in the opposite direction - my character's ragged breathing and pounding heart serving as the soundtrack to my hasty retreat.
After that, Slender turned into a back-and-forth battle between my brain and my eyes. "Something just moved over by that tree! I'm sure of it! Oh god, it's all over." "No, no, calm down. You're just seeing things." "Well duh, I'm seeing things. I'm a pair of eyes. That is literally all I'm capable of doing." And so on. The Slender Man just sort of appeared in places, though - I never caught him in the act of movement - making it all the more terrifying. So unnatural and unpredictable.
Eventually, I emerged from some kind of public bathroom facility, briefly turned to look back, and then he was right in front of me. I definitely yelped, only it sounded more like "Eeeeeeeeeek." Then there were a bunch of ghastly noises and that was game over. So Slender's definitely a one-trick pony (with disgusting elongated limbs), but it's a fairly decent trick. Give the free beta a go here and gain an exciting new thing to constantly glance over your shoulder in fear of.
Or, if you need more convincing, here's a quick trailer.
Thanks, Indie Games.