This movie places high value on romance and the concept of true love -- Ariel is so enamored with Prince Eric that she sacrifices everything, from her family to her voice, in order to be part of his world. Many think this storyline is problematic because it reinforces the idea that a woman should give up her pursuits and opinions in deference to a man. But others can put this concept aside to enjoy the sweetness of the central character and the universal challenges of love. Other themes include curiosity and perseverance.
Ariel's father is imprisoned by the cruel sea witch, Ursula, who also grows larger than a ship and tries to crush it wielding a giant trident. Ursula brags about all the mermaids she's imprisoned and those "poor unfortunate souls" are shown shrunken down and sad. A French chef runs around the kitchen after Sebastian the crab with a cleaver and merrily chops up other fish. Eric almost drowns when his ship sinks in stormy waters. Ursula dies rather dramatically in the end.
The entire movie revolves around Ariel's crush on Prince Eric and her desire to be with him. One sweet-natured song is all about getting a kiss out of Prince Eric.
Ariel is a very popular Disney princess, whose brand reaches far and wide, with princess branding on consumer merchandise, food products, etc. as well as in books, websites, and other media.