One complaint I had about this movie was that the 26-year-old Queen Ariel looked a little bit different from the 16-year-old Mermaid Ariel from the previous movie, which is entirely appropriate because it's been ten years and she's a mature woman now, whereas she was just a teenage girl in the first movie.
But then, as soon as she steps back into the sea and turns back into a mermaid, she looks exactly like her 16-year-old self (minus some animation quality). I thought she should have looked different. More MILF-like. I'm not exactly sure how to convey that, but that's the animators' job to figure out. Maybe leave her hair tied back? Give her a different top (maybe have her put on a normal human swimsuit before jumping into the water)? I dunno.
It's like, the movie felt that the audience just wanted an excuse to see Ariel in her shell bra and fins with the floaty underwater hair again, where I was interested in seeing an entirely new side of her. If people want more of teenage Ariel (and hey, I got no problem with that) there's the TV series (hey Disney, when will I ever be able to purchase that?) or the prequel movie (which would've had more impact if it was a return to teenage Ariel after an absence).
I suspect that Ariel was also mentally acting like a dumb 16-year-old in this movie where she should be acting like a grown-ass adult, but it's been a few years since I've seen this movie (and I probably lost most of my braincells when they built the wall), and the visual of seeing Ariel become her previous self unchanged was what stuck in my mind as really bad.