I obviously don't speak for everyone - especially since I don't actually dislike the character designs from TH per se - but I do consider them to be a downgrade from some of the previous games. I dunno, the characters have a sort of... plasticky look to them. Like a weird sheen coats their bodies. I don't know how to explain what I'm talking about - I'm not an arty person, so I don't have the vocabulary to express what I mean here, but I found it off-putting.
My bigger issue with TH is actually how stiff the character animations are outside of combat, and how chunky the world is.
For what it's worth, I think Shadows of Valentia was the peak in terms of the series' character designs. Kinda wish we'd use that style again, it's really good.