For the discussion about making killing in an FPS unsatisfying: Dwarf Fortress's combat in Adventure mode would actually be pretty horrific to somebody who wasn't used to it. Fighting against human(oid) enemies isn't really unsatisfying, it's just that it's never as simple as stabbing them until they fall over and die cleanly. It's really a combination of the realistic combat and intense difficulty. Once you disable an opponent, you'd better move on to disabling the next one or you'll find yourself surrounded. Eventually, when all the bandits/kobolds/whatever are bleeding out and unable to fight back, it's a matter of going around and cutting their throats so that you can loot them and leave as quickly as possible. It's still fun in a certain sense of the word, but it's definitely grim.
It'd be harder to implement in an FPS, though. Maybe have it so that enemies aren't guaranteed to be die just because they fell down? They're out of the fight but still alive, moaning and clutching where you shot them. Since they're on the ground, you're less likely to notice them until after the fight's over, giving more time to notice that they're just lying in pain on the ground.