I should probably clarify, I don't intend this to be a "everyone's constantly fighting" type game. That's just the central conflict. There can/will be other plots, characters can create relationships (of any sort) within the Hunter/Mutant groups or between groups (Mutants capturing Hunters and vice versa). There can even be pacifist Mutants, though pacifist Hunters might not work so well. :)
A few more notes:
Four years ago, when plans to recolonize Earth were being finalized, the Solar governments began advertising for scientists and mercenaries to be the first scouts and cleansers. Roughly 100,000 applied and were accepted. They were collectively called Mutant Hunters and sent to Mars to await transportation to Earth. These Humans hardly constitute a cohesive group, though. Each is responsible for providing his or her own gear and decisions on what to take vary widely. All of the Hunters have been assigned a zone to clear, usually a hundred to two hundred square miles or so each. Some prefer to work alone, others have formed teams of two to six members. Many have plans to set up a base camp, others plan on moving every night. There is no uniformity, save that every Hunter has been briefed on the current state of the planet and the known classes of Mutants. The first group of Hunters was dropped three months ago with replacements coming in every month, usually only a hundred at a time.
Humans average 150 years with “old age” hitting around 100.
Left alone for a century, the Mutants created before, during, and after WWIV have been prolific. According to estimates, there are now over a billion of them scattered across the globe. Most congregate in tribal or other groups under the lead of various chiefs and warlords. Some live alone, though. While the Hunters are technologically superior, the Mutants have numbers, knowledge of their territory, and strange powers on their side. Technologically, they are backward with some combustion engines and firearms (think Mad Max technology and society). They are also infinitely variable, the classes and species below are the tip of the iceberg. Finally, Mutant lifespan varies by type, most are within the Human norm, though a few possess greater longevity or shorter lifespans.
To help the Hunters prepare, the Solar Governments put together the following list of classified Mutants (this is by no means a complete list):
Animutants – basically anthros/furries.
Morphs – shapeshifters
Mutimals – mutant animals (generally non-sapient)
Phreaks – psis
Rocks – tough, strong mutants, usually not that bright; generally ignore paralysis and stun weapons
Squids – tentacled mutants
Cat-Girls – Animutant felines, housecat base
Dogboys – Animutant canines, usually German Shepherd or Doberman base
Gargoyles – Cowardly Rocks with incredibly tough skin and wings
K’tulus – Squids whose tentacles surround their mouths, otherwise humanoid
Mutimutts – Canine Mutimals, typically horse sized St. Bernards
Octos – Squids whose tentacles replace their arms, usually possess six or eight.
Odos – Morphs who normally exist as a gel but can assume any form
P-Tigers – Tiger Mutimals with limited telepathic ability
Teeks – Telekinetic Phreaks
Teeps – Telepathic Phreaks
Trolls – Very strong, tough skinned Rocks
Weres – Morphs who normally exist as humans, but can turn into animals and/or hybrids, usually only one species