To be perfectly honest, Slender Man lost me within the first ten minutes. I found it pretty dull and boring at the beginning and it did not pick up much after that.
The latest horror film is based on the urban legend of Slender Man, which was another issue I had with the film. There was a real case of young girls injuring another girl because of their belief in Slender Man so it is tough to create this fictionalized version of the film. That does not mean that there couldn’t have been a version of this that would have worked. Maybe if it dealt closer to the psychological aspects instead of mystical it would have been stronger.
The acting in the film was, at best, competent. It felt like all the three to four girls were doing in the movie were checking their phones or screeching. There was not much in way of subtlety here.
There were also way too many jump scares in the film, falling back on the old trope really hard. The music would get loud as something was about to happen and that is a technique that really needs to be handled with more of a light touch these days when you are getting top notch quality horror movies that use only a limited amount of jump scares.
The story was needlessly confusing and difficult to follow. The characters were underdeveloped in almost every aspect. There was really no lead protagonist throughout the film -kind of bouncing that around. The final act had too many unintended laughs in it to be effective.
I do like how they used the Slender Man through most of the movie, keeping him in the shadows and hiding the appearance of the creature. That was tossed out the window in that third act though and not for the better.
These days you have to elevate your game if you want to do a horror film and Slender Man did not accomplish it. Go watch the documentary on the real life story if you are having an interest in the Slender Man because it is a better portrayal.