Major pet peeves when it comes to character designs?
Those are honestly the first things I notice. Stuff that’s oversaturated, too dark, unnecessary contrast, uses a lot of rainbows, or has just too many colors in it in general.
Also lack of any emphasis in the design kinda can bore me. Exaggerated hair, arms, frame, chubbiness, hell even stuff like the butt or boobs or muscles can be great if emphasized properly. Without flaws or exaggerations or even just a flow/consistency to the design, there’s not a lot of uniqueness.
One final thing is more just a lack of purpose or motive. Even if it’s just a simple, unimpressive goal or even something behavioral, it’s still good for a character to have SOMETHING to work or look forwards to. I like a reason to root for a character (or conversely to chastise them).