Me too. I still think that pavilion is one of the best things Disney has ever built as a whole experience (hydrolators to SeaCabs to the seabase). I thought about it regularly as a kid. It's so disappointing that that awful Nemo ride is there now instead.
The Nemo ride in and of itself is OK. It is the fact it replaced what I consider "real" imagineering is what is disappointing.
Seabase Alpha was just an awesome idea. It must have been some great brainstorming.
Well, what else can we put in EPCOT? How about an aquarium?
But aquariums are so run of the mill.
How about we flip it around? The people are inside the enclosure, at an undersea base.
Yeah, they have to take an underwater elevator, yeah yeah a hydrolator!, down to the base.
What if they didn't go right to the base, but went to a staging area, where they then had to ride a train (hydrotrain, seatrain, SeaCab, yeah, SeaCab!) through a clear tunnel to the main base.
It was just a glorified aquarium, but combination of story, and tech, and effects is what made it great.