The objective seems simple enough to begin with: for every person that you let through the border (assuming they have the correct paperwork), you'll be rewarded with a small amount of money. You'll need this money to keep your family warm and fed - that's Papers, Please.
Well not quite. Your meagre income isn't going to be enough and by the end of your third or fourth shift, you'll have already needed to decide between medicine for your Mother-in-Law, or food for your entire family. Those are some pretty awful decisions to be making, which is why the alternatives will seem so damn appealing.
Your descent into terribleness will likely start with a few rushed passports. There's always a time limit to worry about and you're only getting paid for the people that you let through; staying vigilant can be difficult when you have a family to feed. Alright, a few mistakes are made and maybe that means some people pass through the border without the right paperwork, but that's just a risk you're forced to take.
How about bribes then? Is that too much? It sounds pretty wrong, but maybe it's just the system that's wrong. Some of these people sound really hard done to and you could really use the extra cash about now...
The guards have an interesting proposal that might help. For every couple of people that you detain, you'll receive a little bonus from them. You were having to detain people already anyway, so what harm could it do? I mean, sure, you might start thinking twice about letting people get away with the smaller crimes from now on, but it's their fault for not having their papers in order. Right?!
By the end of your time with Papers, Please, you'll likely feel that you can justify every decision that you've made. Yet as you step back and view at them as a whole, you might be surprised and just a little bit horrified by what you've done along the way. It does all of this whilst convincing you that you're playing a game about checking dates and photographs. Superb.