Horizons. It was my favourite ride as a child, and I still remember the magic of it vividly.
Jeremy Irons and his monologue in Spaceship Earth -- the script was SO much better than tripe in the current ride. It angers me to hear "the World-Wide-Web" and all that crap... I just don't want Epcot to be dumbed down and that's what it feels like SE is doing, to attract a larger audience, maybe? It's frustrating to have knowledge de-valued. And not, of course, to say that the Internet isn't a fount of knowlege -- but just that I think SE is now "trendy" and before, it valued history and did not try to be "cool".
Expedition Everest, Splash Mountain and other beloved rides not working properly. The lack of maintenance and upkeep and the LOVE going into the rides and the 'show' is what I miss the most when it comes to the current WDW. There is a lack of Walt in the proceedings and a lack of remembering what meant most to Walt that I feel keenly when I visit Florida's parks.