I would say it’s a very captivating grim dark thriller / slasher, but with a few noticeble drops in quality.
Some of the kills look really poor overall (bathroom scene is the worst offender, blood effects very clearly were added later in After Effects), the image in some handcam scenes wasn’t stabilized, the ending is a cliffhanger (the sequel is already in production though) and also sucks, plus it was spoiled in the beginning of the movie for some reason, which was a letdown and I wish they wouldn’t do that. The Santa killer behaves like a supernatural poltergeist (FBI scene is creepy but not believable anyhow), TV scenes could look more authentic. All local town characters are degenerates except sheriff and his helper, but we all know it’s actually a good thing for mass murder killing movies – you don’t care because you don’t connect with such characters.
What’s really good about this movie, is actually the plot and the way the mystery unfolds – it’s really interesting to follow a story trying to guess who are the killers.