Comparing Troll Hunter to the likes of The Blair Witch Project, Cloverfield and Diary of the Dead is inevitable given that the filmmakers present it mockumentary style as having been constructed from found footage shot by their diegetic counterparts.
The conceit is believable, with the single hand-held camera based aesthetic working well barring a few moments where the cameraman’s point-of-view seems more about getting that shot than staying alive. The CGI trolls are seamlessly integrated, the human performers believable, and the illusion strengthened by the filmmakers avoidance of non-diegetic music.
While they don’t shy away from showing the monsters, much of the running time is spent searching for and learning about the trolls, with their ecology and the reasons no-one believes they exist surprisingly plausible.
This said, the film has certain essential problems: It isn’t doing anything that hasn’t been seen or done before, beyond the use of Norwegian locales and myths. This in turn may limit its acceptance by the sort of mainstream cinemagoers who might otherwise appreciate it, especially as it isn’t particularly scary or gory for a horror film. The chances for a Hollywood remake are likewise less likely because it is so culturally specific.