-It's reasonable to call this a "dumb home invasion film," but I'll give credit for the social commentary stuff...sort of. On one hand, the film's making a point about social inequality, how the rich can ride out the poor while the poor and homeless are cannon fodder, but on the other, it does this with the subtlety of a jackahmmer. A better writer might have let the theme seep in (the wealthy Sandins taking in a homeless man, the disparities becoming clear over time), but no, this theme is established right from the outset, and done over and over via radio conversations. So, props for the theme, minuses for how basically it's conveyed.
-So if this is a gated community, how did homeless guy (I checked the credits, he has no name) get in? And how did the college kids get in?
-The movie really has a problem with pacing, and it's made all the more apparent given just how short it is (around 90 minutes). There's a lot of time of just sitting around at home, and after the guy is let into the house, a lot of time searching for him. I could call it a slow burn, but it's arguably burning too slowly.
-Credits to blonde college kid - he does terrific acting with his facial expressions and other mannerisms. His lines (e.g. "send out he [homeless guy] or you [the family] shall be thee [guy I've just shot]) by all rights should fall apart, but he manages to deliver them with such conviction that they work. Though on the other hand, their plan makes little sense. "We'll give you time to find the guy and send him out to us. In the meantime, we're going to cut the power to your house, which I'm sure isn't going to make things more difficult for you").
-So, the whole "what have we become" scene is well done. Within the family, I think Lena Heady does a lot of the heavy carrying, or at least, is easily one of the best actors in the film.
-Okay, so, you've decided to defend yourselves against an army of college students, and you're breaking out the heavy guns. Great! You're going to give a gun to the homeless guy, right? I mean, sure, he's put a gun to your daughter's head, but given the scenario, it's practically guaranteed he'll be fighting in your corner and...um...you've left him tied up...
...idiots.
-What follows is a mixed bag. The pool room brawl/gunfight is well done, but other stuff? Meh.
-So again, when Lena Heady's character begs for her children's lives, or at least to hold them while their psychotic neighbours hold them hostage...damn, it's some great acting.
-So, homeless guy is going out into the world, and Mary asks is he going to be alright. Well, he might be if you, I dunno, gave him some money? FFS, this guy saved your lives (granted, you saved his as well), and you were discussing buying a yacht earlier in the evening, I think you could spare a few thousand.
-Come to think of it, if someone is killed on Purge Night, does the family get to claim life insurance? I mean, the film's making a point (however unsubtly) about the Purge driving up gun sales and security systems installations, so, just wondering.
Anyway, yeah. Film's stupid, but has some intelligence, and just manages to scrape into "good" territory.