The original Purge was a good idea for a film. If it was made thirty-five years ago by John Carpenter in his prime, it would've been fantastic. Think of Escape From New York and you'll probably see why I suggest Carpenter would have fit so well.
Sadly, as it was made in modern times, the initially thrilling concept of a single day of the year when all acts are decriminalised, was run through the idiot filters and the three purge films have shit into the cinemas to the delight of cretins.
That said, I've watched all three and this one was probably the most entertaining.