To me, one of the funniest and most interesting things about the look of Spock is that he's so quintessentially 60s in his look.
Specifically, he's so incredibly Mod!
To the point it explains nearly everything about why he looks the way he does. Because if it ain't Mod then it's basic geometric design principles.
The Mods, or Modernists, were a British music based subculture of the 1960s with a heavy interest in jazz, poetry, and fashion. Which are interests Spock is even shown to have in the series.
In Charlie X he's shown to have a spontaneous jam session with Uhura, which is a key component of jazz.
In Catspaw he's shown to have an interest in and opinions on poetry.
In terms of his physical appearance, it's also extremely mod! Just look at his hair and compare it to The Beatles (the biggest band of the decade)
His eyebrows, makeup, and eye shape were also very influenced by 60s ideals. With bold blue eyeshadow, thin eyebrows, and downturned puppy dog eyes being extremely popular in specifically women's fashion.
Just look at Twiggy, the most popular model of the decade! I also added a makeup diagram from a magazine to further show it
Beyond Mod aesthetics, a lot of Spock's alien look can be broken down to basic design principles around geometry and symmetry. Which are details that can easily go unnoticed if you aren't keeping an eye out. I didn't notice until I started drawing and painting Spock.
In particular, the curve of his eyebrows mirror the natural curve of Nimoy's hooded eyes, which makes it feel very visually natural for the character.
Additionally, the angle of Spock's eyebrow, the curve of his ear, and the cut of his hair are BRILLIANT in how complimentary they are. The eyebrow flows to the corner of his haircut, the ear creates a beautiful arc leading into the angle his bangs are cut. (It's so well balanced that I have a headcanon that Vulcan art and beauty value the face in profile rather than straight forward, but that's a whole other discussion)
It doesn't feel like prop makeup when it's so visually cohesive for the face!!!
Here's some poorly drawn diagrams to show my point
Overall, I think one of the most interesting aspects about the design of Spock is the sense of androgyny he encapsulates when capturing 60s fashion ideals. While undoubtedly masculine (and with a popular men's haircut), his makeup, styling, and body type better reflect the fashion ideals of Mod women in the era.
I think this androgyny is part of why he's a sex symbol of sorts. Women have historically shown an interest in men that escape the bounds of what is considered traditionally masculine for their era. After all, if a man is shown to positively embrace characteristics associated with the feminine, then he's hopefully less misogynistic than his peers.
Finally, I just wanted to acknowledge the model Patti Moffit, because I don't think there's another person who can better show the incredibly 60s aesthetic of Spock more than she can
Because at the end of the day Star Trek will first and foremost always be a show about the 60s