The villains for this series have such great and creepy designs. I don't know if anyone else feels this, but there's this genuine feeling of unease when I see them. I never got that from any other shonen. Naruto's Orochimaru sometimes had this in his most freaky moments, but it was rare. I think Bleach attempted it with Aizen's final form(s), but for the most part they were designed to look cool. MHA do look cool, but also legitimately scary.
He definitely draws out a different art style with villains. It's effective, but also reminiscent of western comics. It's very sketchy, with thick, erratic lines. But other times it's just way more detailed... which feels unnatural in manga. Definitely know what you mean when you say "unease". Some of his panels remind me of horror manga.
This will always be such an effectively creepy panel:
And this: