1) There are two kind of horror movies. The scary ones and the ones which can be called : "A fun ride". I like both of them. THE SACRIFICE GAME is not scary but it is a fun ride. Enjoy it for what it is. I appreciated the fact that there were no cheap jump scares. Characters were not making stupid decisions either. Everything felt natural, at least for a horror movie. Ok, a specific character made an absurd decision towards the ending but it is not something unusual for this genre.
2) Another positive here : There were likeable characters. And the villains were really evil and you were rooting for their downfall. I can't stand watching a horror movie in which every character is disgusting or unlikeable and you kinda root for the villain to kill them all. Things are pretty clear here. Of course, there is a big twist but still, it made this movie more interesting.
3) Acting is above average for a horror movie. Georgia Acken can be a great actress in the future, her role was the most demanding. Of course, this is not the most convincing and realistic movie of the world and viewers won't feel anxiety and agony, but there is no need for nitpicking. It's a horror movie.
4) This is not a MUST WATCH movie, it's not scary neither exciting and if you think about it, you will find a lot of flaws. (For example, the whole thing about the photographs and a specific person..). Lower your expectations and you will enjoy it, some reviewers are unnecessary harsh. This is a movie that respect its viewers.