Personally... well, to be honest, I wish it focused more on the father than the other characters. The others - especially the sibling duo - were mind numbingly, audience-insultingly dumber than a bag of hammers. They fall in the same trappings as your garden variety moron in horror movies, it was annoying.
Meanwhile, the father's character arc - before the final act and he was relegated to just a measly antagonist - was interesting. It was a fresh spin on the usual Slender story and it could have been genuinely tragic. There was something good there, but it was under-utilized, untapped, unfulfilled.
Still, this might have some of the best special effects in any Slender Man story out there, on par with TribeTwelve. Damning with faint praise, I know, but credit where credit's due.