If you enjoyed the original Slender game, check out Slender: The Arrival. It is a revamped version of the original. It is created by the same person who deveoped the original Slender, but also adds in the talent of the Marble Hornets staff to help flesh out the story further. It is more than just the 8 pages in the woods game, as there is much more story this time around and multiple levels. You can preorder the game for $5 and you also get access to the Beta. The Beta is just an updated version of the original with much better sound effects, graphics and lighting. I suggest anyone who is a fan of the original to check this game out.
Its horror because its scary as shit. The graphical enhancements in Slender: The Arrival make it even scarier, because you're in a forest at night, with nothing but a flashlight, and some man in a suit is following you the entire time, only you never know where he is, because he doesn't actually chase you. He just appears at random as soon as you feel bold enough to look out the corner of your eye.
I didn't find it as good of a game as I found Amnesia or Penumbra for example. I've played SCP as of recent and I've enjoyed it (it's FREE). http://www.scpcbgame.com/
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Just scares, so no, it is not a horror.
http://www.scpcbgame.com/