Interesting horror premise needs to be worked out more

Rating: 6/10 (3 May 2014)

It's 2022 in America. Unemployment is at 1% and crime is at an all-time low except one night every year. The law allows many forms of crime including even murder in that 12 hour period. James Sandin (Ethan Hawke) sells home security and is having his best year. He has gathered his family (Lena Headey, Max Burkholder, Adelaide Kane) to wait out the night. Things don't turn out well starting with the daughter's boyfriend. Then the son allows a vagrant to enter their house who is followed by a mob intend on killing that homeless person.
The premise is interesting and original reminding me of Sparta and the Helots. It's certainly a good way to get into a horror movie. However there are a lot of aspects that went uninvestigated in this movie. Everybody has enemies and it's an obvious avenue to go for. For example, he's the best salesman which seems to me to be an obvious reason for other co-workers to kill him. Writer/director James DeMonaco just didn't think through all the possibilities in this world.
The obvious fix is to make the purge be only against the poor and the helpless. There could be rules about harboring the hunted. The family lets in that homeless guy which could make them fair game. I'm willing to not harp on it but I must deduct a point for the mistake.
When the power goes out, the darkness is not a good way to shoot a film. However when the mob gets vehicles which could light up the house, the lighting looks good. All the light and shadows provide great horror opportunities. I wish more of the movie take place in that lighting scheme.
Another missed opportunity is the ticking clock. It could have been a great vehicle for raising the tension. Instead the movie wastes this away by sitting around to run out the clock. It's not the most compelling climax.
It's a great original premise with loads of opportunities. With a few more tweaks, this could be a great horror franchise. It has a built-in morality play. The premise doesn't even need any one particular character to carry it either. This could run for a long time if they put in a few fixes.