Basically, humans tend to be the individualistic and practical explorers in a lot of sci-fi...you know, Space Americans. Other races are assigned these far more specialized and homogenized cultures that represent only small facets of our lifestyle. I'm talking about lazy Star Trek tropes like the eternally-warlike Klingons and coldly rational Vulcans.
|Watch out for Space Americans, man|
The same is often true of various demi-human races in fantasy settings, to an extent. So not only are these mythological entities scrubbed clean of mystery by allowing players to run them, but they are further constrained by unimaginative stereotypes. Dwarves are grumpy, greedy, industrious and proud. Elves are elegant and aloof, often advanced but in decline. These lazy cliches have had all the life stamped out of them since Tolkien.
But what if humans were the strange and threatening aliens who belong to a heavily-stereotyped culture? I proposed two possibilities in the thread: humans-as-orcs and humans-as-elves.