I think that you can't actually spoil a good movie, but I also know that many people think that spoilers are rude. This is a dilemma when I'm confronted by a movie like You're Next (2011, directed by Adam Wingard), because many of its pleasures are built around surprising the audience and picking it apart to demonstrate how it works is a bit like dissecting the golden goose. The fact that it does work is also a surprise in itself, given that director Adam Wingard and writer Simon Barrett's previous films have sometimes felt like shambolic, kit-bashed affairs, and this one is constructed like a watch.
Note: I'll try to avoid spoiling the film, but I may not completely manage. You've been warned.