It has been written here in a review that this game is just a pointless waste of time and I would agree, however for my 10 year old it was much more insidious than that. I disagree with the statement that it isn't suspenseful, my 10 year old son found it very frightening and suffered nightmares after playing this game. Some of his friends love it and don't have an issue but others really did.
Please, please do not let your children play or watch another person play this game. I teach coping skills to 7to 12 year old children that have anxiety and depression. In anxiety ratings many children list Slender Man as something they are very afraid of!