Gareth i love that idea. We shoul deffinately hve a universal force such as the god pitting te factions against each other. And of coarse, breaking them down.

Caliban, to answer your questions ill post what i was going to do with these factions.
Humans- were going to be masters of self. They would have more technological advancements that focus on enhancing their soldiers killing capacity and survival. They would lack jets and tanks, but would have exoskeletons and etc. imagine every soldier being like cyborg, or green goblin. They cant do much to support each other (after all we people can be selfish.) so their sciences would be focused in the medical field. They would attack in small groups equivelant to the 30 member squads holstered by the undead.

Elves- would be masters of the natural world. They find simplicit but effective means for combat. They carry more tactical equipment, and do bolster magical ability, primarily alchemy (such as in full metal alvhemist. Where each elf would get one type of alchemy.) though surprisingly, they are often associated with demon worship, which leads people to believe that their powers are actualy signed for with demons! So elves would not be as innocent as the fairy tales make them out be.

Since the elves and undead are teaming up against humans, i wanted to draw a defining line. The undead simply want to survive. (Inverse apocalypse) and the elves want to make sure that the humans never threaten the natural balance of the planet. So humans try to kill undead, undead try to defend (but as you can see, are generally outdone by either race) and elves are trying to wipe out humans. Undead have numbers and teamwork, humans have super soldiers, and elves have powers.

This is what i had in mind, though im of coarse open for change and tweaks. Even different factions. Point is, i want a not too complex story so i can feel like a total bad a** for breif moments. XD any role any person asumes would be as a "hero" for their chosen race. I dont know if we should keep everyone in one race to keep thigs simple, or let people choose different races and fight each other as well.

I also dont know wether this would go under casual rp or arena.