I almost hate to bring the game up again, but Undertale did a pretty good job using a "kill everything" path as the evil route. There are even different forms of it, one is where you just kill everything you encounter through the game and progress as normal otherwise. Doing this gets you one of the "neutral" endings, because it can be argued that everything you did was in self-defense, even if you're a bit gung-ho about the affair. The alternative to that is a genocide run, where you are actively seeking out random encounters and grinding them out until the game stops giving you monsters to fight. Doing the genocide route has the consequence of most of the NPCs in the hub areas evacuating to avoid your wrath, since you're systematically hunting down and killing anyone you can find. The route also has two boss battles that are only available on this particular type of run, and they're also the two hardest boss battles in the game. To go for this route, you have to start in the first area, before you progress and get locked out of it. It's something you have to be deliberately going for to actually get started. Not to say every game should try to do this, or that most games don't fall flat with a kill everything route, but it can be done well.