The atmosphere of the film is great, although there are a few times where the story is just a tad slow. The characters are all fun as well as believable, and the acting is spot on. Where Trollhunter's greatest weakness lies is in the trolls. They really shouldn't have fully revealed the trolls so early on. Maybe this was deliberate in that the filmmakers wanted to poke fun at how most found-footage movies never fully show their monsters, but it really detracted from the film. The trolls would have been much scarier if more had been left to the audience's imagination.
All in all, a good way to spend an hour and a half.