I am a big Star Trek fan. I particularly like the aliens. The Bajorans are the coolest, the Borg are the scariest, Q is the funniest but I like the Ferengi, too. They all have their interesting points. Aliens can have a hive mind or a warrior mentality, be empathetic or totally
emotionless, have two hearts, a tail, be able to change into other shapes, live forever or change bodies at will. But there are limits. They all, apparently, can breathe oxygen, are bipedal and speak flawless English.
This is pretty much necessary as a plot device. They are played by human actors so there is a minimum and maximum size. You can add horns on the head, or weird patterns of facial hair, but they have to maintain, roughly, a human shape. If English were not the lingua franca of the entire universe, you’d need subtitles and the writers would have to work a hell of a lot harder, plus it would be difficult for the human captain to inter-react with them well enough to save their planet, fall in love with the best looking one of them, and break it off sadly at the end as he rides off (metaphorically) into the sunset, all within a single hour, including advertisements.
I believe some day we will escape this planet and travel among the stars. But the reality will inevitably be more bizarre than the fiction. We are land based, oxygen breathing creatures with opposable thumbs because we evolved on a planet which favored these characteristics. Creatures who evolve in different atmospheres will be as different from us as different can be.
So, I wrote this poem about it. Feel free to hurl metaphorical rotten fruit in the comments section.
We have evolved within this atmosphere
this envelope of air, this tiny shell
around the planet we all know so well
We know so well, of course, because we’re here
The rivers flow with water we can drink
the plants that grow are good for us to eat
the surface is well suited to our feet
It couldn’t be more perfect, I don’t think
Yet, as we find new planets out in space
each one is very different from our own
fiery hells or frigid, barren stone
although life could evolve in other places
On different planets, under other skies
the phrase “life as we know it” won’t apply

I’ll save my rotten fruit for something else. That was terrific!