I think the biggest strength here is the presentation, but I do think there is room for improvement. I would add more sprites to help the map feel a little bit less samey all over the place.
I think my biggest problem is that I just don't see the use of theme here. I don't know if Slenderman changed at all during the gameplay. Slenderman only killed me once the entire game and I wasn't sure what triggered him.
One last thing, Slenderman gameplay is gets old really fast. Why don't you add something to spice it up? Since its staring Mr Kravin, why not add a powerup, like maybe a Redbull to make him go fast? Just a thought...