- Awesome Art: The teaser poster for the film has been positively received due to its simplistic nature (particularly the breaks in condensation on the windows subtly alluding to his Combat Tentacles).
- Critic-Proof: A mild case. The film was panned by critics and audiences alike, but it managed to make $30.2 million domestically and $48.9 million worldwide against a $10 million budget.
- Designated Hero:
- Hallie is painfully aloof towards her sister, to the point of refusing to let her hang out with her and her friends despite the fact that it's been made apparent that she had promised to let her do so multiple times, and in the end when she offers to let Slender Man take her for the sake of her sister, she runs screaming when the titular villain obliges her.
- Then there's Wren. While there isn't much to be said about her, she tries to sacrifice Lizzy to the Slender Man to save her own neck and she's only called out on it once, and that was briefly.
- Hilarious in Hindsight: Around 2010, LittleKuriboh released "Concrete Giraffes", which ended with a Slender Man movie being produced (along with Joey proclaiming that Hollywood has officially run out of ideas). Eight years later, and Sony releases an actual Slender Man movie. Naturally, LittleKuriboh took the opportunity to have Marik and Bakura comment on this.
- The main villain of Over the Garden Wall, The Beast, is frequently compared to the Slender Man for being an ominous, faceless silhouette-figure who hides in the woods and preys on children. This movie's version of the Operator turns out to have the same modus operandi as the Beast, turning his victims into trees.
- Idiot Plot: The whole reason Slender Man even bothers with the main cast is because they decide to summon him on a whim. Even though they were constantly warned against doing so.
- Moe: Despite the fact that the movie was rather lackluster, Lizzy remained endearing throughout half of the film due to her rather cheerful disposition. Despite this, however, her Break the Cutie moment isn't too emotionally impactful and played rather unrealistically.
- Narm: Many scenes in the movie count, such as:
- Wren frantically explaining Slender Man as being analogous to a computer virus in a human brain.
- Lizzy going insane over the fact that Slender Man had no face, as it's highly unlikely anyone would go mad from that. Likewise, Wren suddenly finding herself caught up in a hallucination where she has no face, and stumbling around comically.
- Slender Man himself; while the prospect of a demon hunting you down endlessly is a terrifying (albeit simple) prospect in of itself, the fact that Slender Man is basically just a sentient tree and the fact that he uses FaceTime diminishes what little menace he had to begin with.
- When Hallie attempts a Heroic Sacrifice in the climax, she immediately backs out screaming when Slender Man obliges her.
- During the date scene between Hallie and Tom. We are treated to a rather uncomfortable scene of them making out, only for Hallie to suddenly hallucinate Tom having an exaggerated angry face while his head spazzes out. This is never elaborated on or brought up again.
- The opening scenes before Slender Man even arrives. The main characters speak in everything short of "hashtags" and their friendship feels rather robotic. Hell, the whole reason Slender Man started coming after them was because they decided to summon him on a whim.
- The entire reveal of what Slender Man does to his victims, namely turning them into trees; aside from the fact that it comes entirely out of nowhere and breaks the mystery behind the question, this left many fans joking about how Slender Man is a tree-hugger trying to save the environment.
- Overshadowed by Controversy: Slender Man had largely fallen out of favor in the years prior to 2018, not least because of the Slender Man stabbing from 2014. This unsurprisingly painted a target on the film, especially due to one of the trailers featuring scenes roughly similar to said incident, causing many to label it as being in poor taste; theaters in the area where it happened refused to show the film to respect the families of who it happened to. Said scenes actually appear to have been removed from the final cut, leading to speculation of Sony attempting damage control. This has a side effect of making the plot incomprehensible at times, with major characters suddenly disappearing without any explanation.
- Snark Bait: The film has been negatively received by critics and audiences alike for being a film based on an Internet phenomenon that had fallen out of popularity in about 2014 (which wasn't helped by the infamous Slender Man stabbing incident) and was most popular in 2012 to 2014, and also for failing to be a good horror movie. The fact that Sony released another highly-reviled movie that was based on a popular trend that could become similarly dated (and had also released some of the Internet's similarly hated movies) certainly didn't help. It currently holds a 7% on Rotten Tomatoes and a 3.4 on IMDb.Rotten Tomatoes critics' consensus: Slender Man might be thin, but he's positively robust compared to the flimsy assortment of scares generated by the would-be chiller that bears his name.
- Tainted by the Preview: The film's trailer has received a mixed reaction, due to its premise, and also the fact that it looks like a generic horror movie. However, some people were optimistic about the final product turning out to be good, but this turned out to be false.
- They Wasted a Perfectly Good Plot: Putting aside the criticism that the film was released long after the Slender Man hype died away, a movie itself based on Slender Man and taking the established mythos and playing around with those tropes into something new (ala Marble Hornets) would have given the film a boost, albeit a little troublesome considering the implications of the character following the 2014 incident, but alas.
- Unfortunate Implications: Less than a day after the first trailer was even released, the film was immediately accused of cashing in on the above-mentioned Slender Man stabbings given how the trailer featured a few scenes that bore some similarities to the incident (such as as girl stabbing herself in the middle of a classroom under the Slender Man's presumed control and drawings that resemble those made by one of the schoolgirls). All movie theaters in the area where it happened refused to show the film.
YMMV / Slender Man