Surprisingly a decent film that is bogged down by some weak acting and bad pacing. There were about three points in this film where I thought it was the end, and yet they found even more scenes to cram into it. Despite this, it never really felt bloated or had any really boring stretches. The dialogue ranged from slightly shitty to just barely competent. The film does not short change on the action, however. Overall, a pretty entertaining summer action flick.
I was going to say that this film was way too late, but I think it still would have been pretty pointless if it had been released at the peak of Slender Man's popularity. Slender Man is neither scary nor a compelling character in the slightest, and the bland one dimensional protagonists certainly don't pick up the slack. Bad writing, bad CGI, and a character that lost relevancy years ago make this somehow worse than the Bye Bye Man.