The Little Mermaid - Ariel's Undersea Adventure has been operating at Disney California Adventure for just about three years, and it just recently reopened with some major changes. The ride got some additional characters in certain scenes, but the major changes come from the way the omnimover attraction is lit.
The screen shot at the top of this post is from a video of the ride as it was from opening until recently. You can see that the lighting is pretty bright, and really shows off the plastic nature of the fish. The one just above this text is from the ride after the recent redo, and it's clear that black lights are now being used to give the cast a 'traditional' Disney dark ride feel.
Here's another that really shows off the changes. Above is one shot of the large room in the center of the ride where "Under The Sea" plays, with a full cast of underwater characters singing and dancing along. Again, this was before the changes and the normal lighting has several glares showing off of the octopus' head.
Now after the changes the mood is much different, with each character really standing out among the darkness. And you also have to remember that black light never looks really great on video, at least in my opinion, so the ride probably looks significantly better in person.
There were some other changes to the ride that included giving Aerial some real hair near the end of the ride - that follows a change to her hair a couple years ago for the "Under The Sea" scene. It's strange, I don't think any Disney ride has ever had so much attention paid to character's hair!
If you'd like to ride along and see just how different the attraction feels, first watch this old version point of view, then click here to see a upgraded version. Right now I believe the changes are only in the California version of the ride, I wonder if they will be added to the Florida ride eventually, too?