Dominions 4 has some interesting effects relating to death magic.
A dominion of death lowers income and causes population loss across the board lowering income for everyone.
A "well of misery" that bestows the caster with considerable resources for death magic rituals, but acts a global misery and illness syphon, slowing the spread of disease, raising happiness and taxation efficiency, etc.
"Burden of time" causes -everyone- in the world to age extraordinarily quickly.
Ideas like this, and perhaps playing into Death as an aspect and champion of natural growth and justice, the passage of time, the judge and executioner, rather than a pure malevolence that wants to replace humanity with the walking dead... that angle might result in a more interesting Great Old One.
After all, Death created time to grow the things it would kill. When the world is ash and everything is dead, death has defeated itself.
Death's agents, rather than grow ever more powerful, should opt to "join their master" once they've become true disciples. His greatest servants become the soil which will grow the food that will feed his disciples that will become the soil...
Death should revile healing and the sciences.
Death should view the undead as an abomination.
Death has no enemies, nor does it play favorites. It will take you no matter how much you love it or how much you hate it.
It's win state is the undoing of the sciences, the return of mankind to its natural state of savagery, beasts that eat and sleep and shit and procreate. To break man's yoke over nature, arrest its dominion over the course natural law.