"Angel of Disease - player starts supercharged, but loses life down to 10%-20% (5-10 HP if Ironman=0). Gains small amounts of health when kills (up to 200%? 150%?), making for a sadistic, morbid angel ;) I'm not sure if he should gain normal health from globes and medkits. Also, it might make Nightmare a little easier, but on the other hand, only if you're ALWAYS killing, avoiding no-one and not holding back."
Making him unable to heal but gain health from kills is too-much of a directly easier version of AoMasochism.
I don't know if my idea's much better, but in any event I suggest at least partial health from kits'n'shit, and more importantly, life-loss to a critical point at all other times (making at least part of it directly more difficult than AoM).