I've been getting really into Vampyr (the video game) recently, and I think the way it's morality system is constructed is quite interesting, and also is one of those things that should definitely be taken up by other game devs and played with.
I haven’t finished the game whatsoever, so this is going to be nature spoiler free!
You have two choices when it comes to every single “citizen” (is. People who aren’t immediately trying to kill you): let them live, or drink their blood and kill them. Killing them, in two of the three modes of the game, is the most efficient way of leveling up, but it also can destroy entire districts because, for example, if you kill all the doctors then no one can get treatment. But there’s a good reason to get that extra xp: enemy difficulty ratchets up very quickly, and it can become very difficult to defeat bosses if you’re not acquiring xp through murder.
This is what your character needs to survive.
Personally, I think it would be very cool to have a game where the “easy” path (killing people) turns the game into functionally resource management—keeping the world from falling into chaos while also gaining power through blood—while the “difficult” path (not killing people) is a much more linear experience. (And I’m not just talking about Undertale!)
And then, of course, there’s the reverse, which I feel like is much less common, where killing people is actually the much more difficult path, and not murdering is the apparent path of least resistance but where there are long-term consequences.
I really like games where everyone, including the people you kill, has a face. It makes things much more interesting when the character you’re playing (who in Vampyr is a specific person, Jonathan Reid, not a self-insert) has a concrete personality and reasons for their actions in that way, although I also greatly enjoy more self-insert-type rpgs.