Come to think of it, that means they're very much humans in funny suits. The alien isn't different because he's an alien, he's exactly like a human but just represses it.

They did a somewhat better job with Commander Data, I think, although from what I recall he tended to act like they were taking human as a point of departure and adding or subtracting features. Also, interesting, he was completely aware of every difference between himself and humans, although since he "grew up" completely immersed in human society that's not entirely unreasonable.