Astronaut: Navigation! Where are we?
Kevin Murphy: Well we're over the Planet of the Apes, approaching The Phantom Planet, right near the Planet of the Vampires which is right across from the Prehistoric Planet.
Kaidan: I haven't spent much time with krogan before, Wrex, and I have to say, you're not what I expected.
Wrex: Right. Because humans have a wide range of cultures and attitudes, but krogan all think and act exactly alike.
Listen, ladies. If you want a problem talked to death, ask an asari. If you want a problem shot, ask a turian. If you want a new problem, ask a salarian. If you want a problem solved, ask a human.
—Renegade Shepard calls 'em like (s)he sees 'em.
Warden: Tell me about the qunari.
Warden: I wasn't expecting that.
Sten: Get used to disappointment. People are not simple. They cannot be defined for easy reference in the manner of: 'the elves are a lithe, pointy-eared people who excel at poverty.'
No one would suggest that a Klingon would be a good Ship's Counsellor or that a Berellian could be an Engineer, they're just not suited to those positions. By the same token I don't think an android is a good choice to be Captain.
— Christopher Hobson Star Trek: The Next Generation, Redemption Part II
The crew of the Enterprise discover a totally new lifeform which turns out to be a familiar old lifeform wearing a funny hat.
Most of Israel’s critics, especially abroad, see the country as a one-dimensional monolith. As they see it, all its (Jewish) citizens are marching in lockstep behind their rightist government, consumed by a dark ideology, supporting occupation and settlements and committing war crimes. This, by the way, is a mirror image of the admirers of Israel in the world, who also see Israel as a one-dimensional monolith, with all citizens marching proudly behind their brave and determined leaders – Binyamin Netanyahu, Ehud Barak and Avigdor Lieberman. The truth is far removed from both these caricatures.
The Kirk: Is it... an alien?
Alien: I. Am. An. Alien!
The Kirk: Oh, right. So whats's The Thing about you, then?
Alien: It's that we'll try to eat you after a bit.
— Mitchell And Webb, "Space Trek And Wars"
Leader of Fedex 11: It is time to meet your end, earthlings! We thank you for being weaker and dumber than us, and allowing us to steal your secrets so that we may rule the universe's delivery business!
Leela: But why do you even want to?
Leader: Hey, everybody's got their "thing". We love shipping and handling, all right?
—-Futurama Comics #2
Nonhuman fantasy races tend to have their differences from humans defined not just physically (pointy ears and what have you) but psychologically. You might think this would entail making them really alien but that's difficult and often winds up making them hard for the average reader or gamer to relate to. What it more often means in practice is that members of the imaginary race wind up all sharing certain personality traits in common. ALL elves are tree huggers, ALL dwarves are dour, stubborn, and acquisitive, etc.
And that makes it tough for the writer to have the critters seem like there are significant personality differences among them. I know, I was constantly trying to solve this problem while writing my drow novel.
That, I think, is, from the author's point of view, part of the appeal of what I call Chinese menu fantasy, where the Tolkienesque band of protagonists has one archetypal elf, one archetypal dwarf, etc. It's much easier to make the characterization work. And I'm not denigrating this approach. I wouldn't dare, now that I've done the diverse band of heroes myself in my dragon thingie.
Of course, there's at least one other advantage to this approach, also. Frequently, much of the point of a fantasy is to give the reader the chance to explore an exotic imaginary world, and by giving him extended commerce with characters who represent many of its races and cultures, the writer facilitates this process.
Astronaut 2: Dude! Wizard planet!
Wizard: It's not a "Wizard Planet". It's a planet with a few wizards on it.
Astronaut 2: That sounds like a Wizard Planet to me.
Wizard: That would be like calling an ocean "Shark Ocean."
''Remember: one culture per alien planet. More than that, and you're just showing off.