Enlightenment for us theme park geeks will be disenchantment for the more casual guests. If I point out the errors, that will be all you will see the next time you ride the ride. But here goes:
I will not really address the compromised storytelling as anyone who has seen the movie knows where it goes off the rails. I will address some more technical aspects of how to properly design a dark ride.
First off, the most egregious error is the horrible use of visual targets. FAR too often the visual targets are above eye level. Which means you are looking up at most of the stuff, especially in the Under The Sea scene. The problem with this is that if you look past the visual target all you see is light rigs and air conditioning ducts. The entire Under The Sea scene should have been sunken at least 4 feet below the plane that the ride vehicles are on so that you are looking down into the scene. That way if you look past the visual targets you would see themed rock work and such. Combine that with the horrible show lighting (FAR TOO BRIGHT) in the Under the Sea scene and you get a not dark room where you are looking up into light rigs and air conditioning ducts. It SCREAMS industrial warehouse, not world class themed entertainment. This poor use of visual targets is not something that WDI's A Team would have done. This is a Theme Park 101 kind of stuff that should have NEVER have happened in a Disney attraction. And quite frankly ruins the ride experience.