This and Robin Hood were easily my favorite Disney movies as a kid, but looking back the story is very episodic and the writing is spotty.
Some of the animation, though especially involving Archimedes and the wizard's duel is hilarious, and the background art, particularly in the beginning and during the underwater sequence is some of the best Disney ever put out.
One thing that bothered me though (highlight to see, because once you notice it you can't un-notice it)
The kid's voice keeps changing, supposedly because they kept having to switch voice actors as they made script changes after their voices broke.