You might look into Savage Worlds. It's a generic system, but it has roots in the horror genre which leaves even high-level heroes vulnerable to a few solid hits. And while it's not level-less... exactly... "levels" in Savage Worlds do work rather differently from what you're probably used to. And it runs fast and simple in play. Finally, there's a wide variety of official and fan-made supplements adapting the basic rules to all manner of different settings, from Weird West to space opera to classic swords & sorcery.