Like I'm sure everyone has seen that viral picture of the cow from an old version of Misa's Realistic Resource Pack:

But more than horrific animals, it's just the mix of genuinely gorgeous texture work in places and some of the most-hostile texturing imaginable. If it were just horrific everywhere it would lose its impact, and if it were just beautiful it'd look like a billion competently bland custom shaders. When you straddle that line though, it just gives it this pristine air of menace and discomfort that I really appreciate in my old age.