So how do Eldar view Space Marines, do they just view them like

They're just human aspect warriors.

In the pathway series they were horrified by the concept of marines as eldar need to wear the aspect mask in order to devote themselves to war and not lose themselves, while marines are always like that

I'm more interested in how they'd view the Custodes. Physically superior to anything in their size-range, such mental conditioning it's impossible for them to fall to Chaos, some of them may be over ten thousand years old.

even more brutish, stinking, hateful mon-keigh, twisted and bloated with crude genecraft and burning white-hot with idiot rage - and far more dangerous because of it

>>54749037
in one book they called them mon-keigh augment warriors, also describing the loyalists as(worshippers of the dead human farseer),

>>54749037
Since they see humans the way we see monkeys, I think they'd just see them as big gorillas. More dangerous then normal mon-keigh, but no more impressive.

>>54753580
So how do they view the Primarchs or Big E himself?

>>54753692
King Kong and Co.

>>54749751

That's a pretty good take on Astartes as monstrous post-humans. We're just sort of desensitized to it due to relating to the human faction and being used to marines being "super warrior monks!" when if we created a marine IRL it would be scary and disgusting.

>>54753692
https://www.youtube.com/watch?v=Tna0QaNg9v0