Resistance: Fall of Man had a crazy hard Superhuman mode. See... in it, you have 4 chunks of health. You can take damage and it will regenerate up a chunk if it's only partially drained, so you could go out, get shot up a bit, then head back to cover, and regenerate back to full health, but if you stayed out too long you'd only have half health or so. On superhuman, one single shot from a bullseye brought a chunk down to a tiny sliver left, so you could only last five shots in rapid fire, basically. I think I somehow managed to beat the first level or two, but it was insanely hard...