Systemic moral choice.
Generally, most games handle moral choices in one of two ways: they either allow you to insert your own personality into a game by giving you really obvious choices (Mass Effect), or they can give you more ethically ambiguous options (The Walking Dead, the ending of Fable II) and force you to learn something about yourself.
In both cases, the moral quandaries are presented to the player as scripted, discrete choices. Save the Rachni queen or don’t. Give food to either Clementine or Larry. Reach a certain point in the plot, then choose one of a finite number of pre-baked outcomes.
In XCOM, however, you deal with these sorts of moral quandaries all throughout the course of normal gameplay. Since your soldiers can permanently die, every single time you send them out into the field you make strategic decisions that also have interesting — if subtle — moral underpinnings.
Say I’ve got a highly upgraded sniper and a rookie who are facing off against a hidden alien. Strategically, it might not be a bad idea to force my rookie out into the middle of the map just so I can draw out that last alien and give my sniper a chance to blow his head off. But what if my rookie dies? I shouldn’t really mind, because I haven’t put a lot of time into him…but I named him after one of my best friends (which, it has to be said, is an infuriatingly smart way to get me to care about a stupid little 3D soldier), and he’s got his own nation, and if he dies I’ll never get him back. Is it okay to let him die to keep my sniper safe?
The terror missions are even more interesting. If you keep your soldiers back and play cautiously, the aliens will kill a shitload of civilians and push you closer to an overall mission failure. If you send your squaddies in guns-blazing, however, you run the risk of losing your troops. Which life is worth more: the civilians, or the soldiers? Are you okay with losing the terror mission to keep your soldiers safe? Are you fine with letting a few innoocent people die so that you can save a hundred more later? Where do I draw the line for what constitutes acceptable losses? At what point do my strategic decisions become moral ones, and vice-versa?
I love Mass Effect and The Walking Dead, but I goddamn adore XCOM’s systems-driven moral choices. They’re less flashy, certainly — a lot of people probably wouldn’t even consider the moments I’m talking about moral choices at all — but they feel a bit more personal because they naturally arise out of gameplay.
You can buy XCOM pretty much wherever. Here’s a video of a dude trying to complete a campaign on Impossible difficulty with Ironman mode on: