As much as Bioshock Infinite had its flaws, I think the reason I like it so much is that it gave me a lot to think about. Granted, many of the sociological issues explored in were things I had given thought to, but the way that they were presented--in mainstream media--created an opportunity for people previously unexposed to the extreme and long lasting impacts of things like slavery, racism, classism, and religion to see how things impacted people. Of course, there are no floating cities (that I'm aware of) but the idea of how separated societies get when there is so much inequality is something that is definitely prevalent in today's world.
In particular a couple of ideas that stood out to me were the implication of religion/religious dogma, the long term effects of racism and slavery, and the disastrous implication of "The 1%". I didn't realise what an exploratory nature of the game when going into it, but seeing how many things people (at least in America) take for granted are actually serious issues is something that needs to... well be not taken for granted.
My immediate focus is religion--me being an agnostic to the point of atheism--and how twisted it makes societies. And by that, I mean organized religion specifically--not that the impact of casual religion, over time imprinting ideas of religious superiority in entire societies, us not enormous--and how it completely destroys people. I'm not going into the whole "how much harm religion does" thing, but Infinite certainly exposes the way people will be horrible just because their religion tells them so.
Also the whole classism and racism thing, and how it is shown in the whole revolution, and division of columbia. I'm not really going to bother going into how provocative the stuff they show is, and what it reveals (mostly about America), but I think that if it doesn't give you something to think about, you need to play the game again.
That also ties into the long lasting ramification of slavery in the US, and how that shows in Columbia and by reflection the modern world.
The reason I love the game so much though is that it's fun, it's enthralling, and it really gives me something to reminisce about. It really made me think. Yeah, it's not the most innovative game, and it isn't quite as ethically challenging as Papers, Please , but what it does do is connect to issues of the modern world, and sends a really important message. And going with my requirements of actually causing me to think, and think about life in general, I think that is what makes Bioshock Infinite such a great game. It's story may be extremely deep and complicated, but it's the underlying key issues that are prevalent throughput the whole that "seal the deal" and make it my game of the year.