If you liked the hugely popular Slender and the Slenderman myth that it's based on, then you might like Slenderman which is a free game that was actually released before Slender.
Different scenario to Slender
Slenderman is slightly different to Slender, however, because rather than being in a forest, you are in a large building. In addition, the concept is slightly different. Slenderman still stalks you, but this time he's accompanied by Slender children (either his own or ones that he's abducted - it's not clear) who can also kill you. However, the main difference between Slenderman and Slender is that you can actually kill Slenderman - and the Slender kids - which is your ultimate aim.
Similar Gameplay to Slender
As you walk around the large building, you can collect a few objects including the all-important gun that you need to kill Slenderman. You can also pick up things like a radio which picks up the electromagnetic interference which tells you when you are close to Slenderman.
If Slenderman or one of his Slender children find you, you can shoot them but you need to keep shooting repeatedly to kill them which means hammering your keyboard like mad. If you don't hammer is quick enough, you die.
Lacks Fear Factor
Slenderman has very basic graphics (even compared to the Slender game) and doesn't quite have the fear factor of Slender. There's no creepy dark atmosphere and it's comparatively boring wandering around a building compared to a forest at night.
Slenderman may appeal to hardcore fans of Slender and the Slenderman myth but it doesn't match up the sequel.