Sea World has changed so much since 21 yrs ago (which coincidentally is when I started going as a regular), it's safe to call it a completely different park. The stadiums and one of the theaters themselves are pretty physically close to the way they were 21 yrs ago, with the exception of the other theater, (the Nautilus Showplace now) which has been enclosed and AC added.
Shark Encounter has went through some name changes and some add-ons and remodeling too. The add on is where the newer entrance is to the attraction, and is nice walk-thru aquarium that has tropical fish and eels in it, then an area that has 3 smaller seperate aquariums. One has Lionfish, one has Leafy Sea Dragons, and the other has Barracudas in it. Then you walk down to the Shark Encounter tube itself. The theater area that you used to watch the presentation on the sharks, then the view screens would lift and the shark tank was there, has been converted into a full-service restaurant called Sharks.
The stingray feeding and petting pool is still there and is pretty much the same exept for some small cosmetic changes over the years. The only 2 food places I can think of that were there back in 85-86(and are still open to the public) are the snack bars in Shamu Stadium and a snack place right by the stingray exhibit which is now called Captain Pete's Island Eats.
All of the shows have changed multiple times over the years and so many new attractions, exhibits, and areas have been added.
The larger additions/conversions to the park since your visit 21 yrs ago are The Waterfront Area, The Key West area including the Dolphin Cove feeding and petting pool, Manatee Rescue, Penguin Encounter, the Pacific Point Preserve seal and sea lion feeding area, the Clydesdale Hamlet/Hospitality House area, The Wild Artic ride/animal exhibit area, Shamu's Happy Harbor area, the Kraken roller coaster, the Journey to Atlantis ride.
All of the restaurants, and almost all the snack places will be new to you too, even most of the gift shops weren't there 21 yrs ago except maybe 4 or 5, I think. lol
There's alot of good things to do and see at Sea World, like the previous poster said, check out their website.
http://4adventure.com/SWF/default.aspx