Slender Man is a modern horror movie reflecting the online myth of the made up character of Slender Man. Slender Man is a creepypasta, which are original fiction horror stories or images, submitted to the internet so they can be seen by other people thereby creating awareness.
Creepypasta is like an advertisement, or a meme, but meant to be spooky, and when others elaborate on it and contribute to the creepypasta, the concept grows. They can be like UFO propaganda, but paranormal, and can be linked to the occult and pseudoscience if the creepypastas derive beyond just human imagination.
Slender Man is supposed to be this paranormal creature that sticks into your mind after you see it, and then it abducts and consumes you, similar to Pennywise the Clown from Stephen King's It or Samara from The Ring.
In the movie, four teenage girls watch an online video that you are not supposed to watch because legend has it that it summons Slender Man. While watching the video, something from the video uploads into the brains of these women causing them nightmares, hallucinations, and a connection with the Slender Man. The film does not explain that much into the mythology surrounding Slender Man though. The edits move too quickly during the explaining processes not giving the movie room to breathe. The writing does not compensate this thin exposition because the writing is thin too when supporting the plot. The characters, bedroom set decoration, music, and location shots all seem to be state of the art. The energy revolving around these four girls plight and their interactions with present day society makes this an interesting contemporary teenage horror film, but any extra commentary into their lives seems to be cut short.
The protagonists never fight or defy the Slender Man and then which helps the plot to easily move along and devour the characters. The relation with the Slender Man to the trees and the wobbling flagella-like limbs fixated with eyeballs makes the film seem to be a creepypasta expansion to the original creepypasta.
The reaction I got from the movie is mixed.
The movie kept up with itself enough for it to get an average C, but nothing else was added for the score to be inflated.