These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Even with the film's Broken Base, Melody did get her share of fans.
Undertow, as well. It helps that he is voiced by Clancy Brown.
Fanon Discontinuity: Neither the Disney company, nor the majority of fans recognize it as "canon". In fact, this movie is most often cited to illustrate the "Disney DTV sequels are animated fanfiction" argument.
Idiot Plot: The movie could have ended faster if Ariel had just told Melody why she couldn't go to the sea. Which is pointed out several times in the film and at the films climax.