First Three Materials! Suggestions and Critique Welcome!

[vlyons20]

Here's my first three materials in designer!  (At least ones that aren't just copying tutorials)
They're part of an independent study for texturing I'm doing through my university and I have this week to revise these three before going on to the next assignment.  Regardless of that though, I'd also like to get them as polished as possible in my portfolio for volunteering with my school at GDC this year.
What do you all suggest I change? (In either the material or presentation format)

Links to each:

https://www.artstation.com/artwork/3oNZvE

https://www.artstation.com/artwork/6a6ZbN

https://www.artstation.com/artwork/Jl2990

[Sarawarreik]

With marmoset I recomend do turntables because video is always more impressive.