Really good watch, would watch again, and can recommend.
First off, Lin Shaye ("Insidious") absolutely steals the scene whenever she is on scene, that lady knows how to "old lady horror" if anyone does.
Like most decent horror movies, this one is fueled by stupid. Even in the unlikely scenario of any of it being real, on top of the unlikely scenario of finding "the game", how insanely bored and out of options would you have to be to do something that involves drawing blood? I had to digress here because it's my main beef with the movie, but it spoils things if I continue.