I know that people sometimes complain that Trek aliens don't always look alien enough but to me I think they kind of miss the point of what aliens represent in Trek. Aliens in Trek tend to represent different aspects of humanity or they represent a different culture or country. They are supose to be human, but humans with a different perspective from earth/starfleet's perspective...
Then why not just make them HUMANS with a different perspective from Earth/Starfleet's perspective? Instead of reducing an entire civilization to a laughable Planet of Funny Hats and perpetuating the underlying notion that it is possible for an entire civilization of millions if not BILLIONS of people to all be defined by a single unique characteristic (e.g. "Everyone on this planet loves to wear funny hats."), why not just project that differing perspective as the defining trait OF THAT CHARACTER?
Or, if you absolutely MUST use aliens -- or worse, forehead aliens -- assign the characteristics at random and use his alienness to get away with some world building:
Option A: "Drax is a Klingon. Drax thinks that war is glorious and is excited about the prospect of combat and violence and he thinks you should be too. When Drax realizes that you DON'T glorify violence and war, he thinks you're a weakling and sneers at you. Drax and his crew want to start a war with the Federation because Drax is a Klingon and Klingons love war. Don't be like Drax."
Option B: "Drax is a Klingon. Drax grew up in the vermin-infested slums of the First City, where garbage trucks make deliveries instead of pickups and raw sewage runs in the streets because the main city -- the REAL city -- is built higher up to avoid the storm drain runoff and the Empire didn't bother to upgrade the drainage system. Drax wants to start a war with the Federation because the Army recruits more heavily in time of war and he has sworn an oath of honor to his clan/family to find a way to bring wealth, relief, or at the very least, a way for the younger ones to get jobs (with the Army, let's say) so the family can survive. Drax is an opportunist with suicidal ideation and a surprisingly keen understanding of how the Klingon Economy works. Don't be like Drax."
Klingon "Warrior Race" ethos can be a background for a character, it can add color and flavor and dimension and background. But once it becomes ALL THEY ARE, Star Trek is accomplishing nothing at all except to train its viewers to project stereotypes as far as they possibly can.
I like how Trek exsit's in a universe were you have all these different culture's who have differences but also have things in common with each other as well.
I like how WE exist in a universe where we have all these different cultures that, every one of them, each produce the same kinds of people over and over again in roughly the same proportions.
And I like a fictional world that reflects this: that there are twenty to thirty different archetypes of people you meet and they're the same people no matter where you meet them or where they're from. Whether you're a kid from Brooklyn or the 84 year old wife of a Pashtun brickmaker, you've probably met at least three of these people:
- The Hero: Moral paragon who wants to save everyone
- The Antihero: Kind of an asshole, but still saves everyone
- The Villain: Complete asshole who wants to screw everyone
- The Jester: Clownish goofball who never takes everything seriously and alternates between amusing and irritating
- The Sidekick: Never has any ideas of his own, just sort of tags along and helps out with stuff
- The Girlfriend: She's only here because she's horny and/or lonely
- The Chicken Hawk: Makes a big noise when thinks are quiet, but hides in a crack in the wall when things get noisy
- The Omnicidal Maniac: Total asshole who wants to destroy everyone and everything (aka "The Anarchist")
- The Fight Guy: Violent temper, loves to fight, thinks you love to fight too, confused when you don't fight him. Wanna fight?
- The Slut: Makes everything about sex
- The Preacher: Makes everything about God
- The Demislut: Wants to have sex with God
- The Alter Girl: Wants to have sex with the Preacher
- The Gangster: Always looking an angle, always manipulating people, never trustworthy
- The Chump: Never manages to find an angle, always being manipulated, always trustworthy
- The Mother Hen: Worries about all the poor defenseless orphans/children/friends/townspeople/neighbors/etc that can't look after themselves and have to be protected.
- The Wolf: Is the reason the Mother Hen worries
- The Raven: "Poor. Impulse. Control." Unpredictable as hell, stopped giving a fuck in third grade.
- The Roddenberry: The guy who has convinced himself that he's really good at his job -- or even is absolutely essential to getting the job done -- and fails to realize that he owes most of his success to the incredible team of people around him (also known as "The George Lucas," or "The Kitchen Nightmare.")
All of these and more should be equally represented in every culture in the galaxy. Their individual backgrounds, evolutionary quirks and cultural traits should give them each a unique flavor, plus the individuality of each character. Otherwise, you're just painting entire societies with the broadest possible brush strokes to the point that it's hard to imagine how those societies could even really EXIST with so little diversity of thought.