Just got back from a quick trip to DCA (love that Downtown Disney parking!) where I rode this twice in a row. Busy Saturday in both parks, but Mermaid had a 10 minute posted wait that was actually 5 or 6 minutes in early afternoon (love that Omnimover without Fastpass!).
The videos here don't do it justice. The first half of the ride through Under The Sea now looks totally different. There's a lot more fish in the first half of the ride, the lighting is tweaked throughout, and there are some new projection effects that look much crisper and clearer than they used to. There's just more going on, more to look at and see now in the first few minutes of the ride.
But the Under The Sea room is now the big WOW! It looks very different, and all of the equipment and rigging in the ceiling is now invisible. You don't even see the ceiling, it just disappears into darkness. Colors and lighting effects now really pop and shimmer in this scene. It's a whole new look and it's fantastic!
This update/refurb/plussing needs to happen ASAP for the WDW version of the ride. They'll never remove Fastpass+ in WDW, but the least they could do is clone this DCA refurb for Magic Kingdom.