How about this list for some inspiration:
i) 1920s Gangsters (cool guns, cool suits, etc.),
ii) Aboriginal (may be limited, but could make a good game),
iii) Matrix-styling (agents & humans),
iv) Druids (similar in scope to Aboriginals),
v) Cops & robbers (could make an amusing game),
vi) Giant insects (would make interesting boss fights),
vii) Romans/Greeks (I'm thinking similar to Assissins' Creed here)
viii) Tiny people (aka Lilliput from Gulliver's Travels)
ix) Decade themes 60s/70s/80s (Some of these styles would look great on screen)
x) 60s/70s TV Sci-fi (I think having chunky sets, and retro fashion in a game would be interesting).
Just some ideas.
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