This certainly wasn't the worst Ron Howard film out there. That's not saying a lot, but since Howard's films can be pretty damn awful, it's at least somewhat comforting to know this isn't one of his ulterior slogs. There's a pleasant goofiness that makes it an easy watch, even when the rest of the film isn't all that great.
As a young boy, Allan was saved from drowning by a mysterious woman. Years later, they find each other again, though Allan has forgotten all about her. What Allan also doesn't know is that the woman is actually a mermaid. The two start a relationship, which leads to some predictable problems.
Hanks and Hannah are pretty decent, the film is quite cheesy but at the same time doesn't take itself too seriously, the pacing is solid, and it chooses its moments wisely to go just a little over-the-top. The rest of it is pretty basic romcom kitsch, very safe and somewhat bland, but you can certainly find a lot worse.