This was the first sequel I'd seen (apart from Return of Jafar) and I honestly thought before watching it that it would be close to the original. I was horribly disappointed.
The storyline was, basically, the first script with a few extra characters and the situation turned around. Ariel and Eric have a daughter, Melody who isn't satisfied with life on land. She wants to become a mermaid. However, Ariel has kept her past from her daughter because she wants to protect her-and when Melody finds out she's upset and angry. And she then decides to run away, and she becomes a mermaid. So she's happy swimming around, and Ariel sets out to find her-as a mermaid.
The story doesn't sound too bad written down, but the clichés and repeats of situations from the first movie are just too obvious. And adding the fact that Melody is, overall, extremely annoying, and the movie becomes almost unbearable.
There's also a whole load of other new characters-Tip and Dash being two of them. They aren't too bad as characters in themselves-just try not to think of Timon or Pumbaa! The songs leave a lot to be desired too, they just don't have the same magical energy as the songs from the original did. The animation obviously didn't have a whole load of work put into it either-in parts it's jumpy, and not much imagination is used for the characters movements.
Another piece of advice-try to forget about Ariel's original character while watching this movie. The beautiful, rebellious, curious teenager has 'all grown up' into a bland, boring wife and mother, and her trademark red hair is all tied up. This is much better viewed if you've never seen the original-you'll have nothing to compare it to.
However, all in all, it could have been worse-it's not as bad as certain other sequels, such as Cinderella II. But it's not in the same league as the original. But it for your collection if nothing else but if Disney go on like this they'll lose all their older fans.