Short, but sweet. Not very sophisticated, but good enough at eliciting that unsettling feeling you wanna capture in horror. The decision not to use the ol' suit and tie on... well, y'know, was well advised, I think.
This kinda demands an expansion of the concept, as I've yet to see the Slenderman Mythos committed to an actual game, even if it's just a mod. Amnesia is pretty much tailor-mad for it. Do some brain storming and come up with something longer. :)