Like many, I miss Horizons and World or Motion. Also, as may be indicated by my avatar I was amazed (and miss) the World Key terminals and main center. I thought it was so cool to make our dinner reservations by video phone to the reservationists.
WorldKey and others, I do remember being amazed in talking to a cast member via videophone in setting up dinner reservations inside Spaceship Earth.
Also miss Communicore East / West, watching TV from around the world via satellite on those mini-TV screens, the very cool poll show, and the ticker the scrolled outside of Communicore.
I miss World of Motion, the bird and robot post-show, and the cool Lean Machine. I fantisized getting one in the future.
Also miss the shooting range and superhuge video / game arcade in Contemporary's basement.
Also miss not seeing Roger Rabbit around the parks (even the Roger and Jessica pins are getting scarce).
Miss the old configuration of Pleasure Island with the west end stage and New Year's Eve fireworks EVERY NIGHT. I miss Pleasure Island in general, especially the Adventurers Club and Mannequins Dance Palace.
Heck, I miss the old Walt Disney Village, Empress Lily, the Village restaurant, and the unique wine shop (though I was not old enough to drink back then).
Also miss Chevy Chase and Martin Short in the Monster Sound Show.
Miss the old tram to and from the Swan and Dolphin to the International Gateway back entrance to EPCOT.
I miss the original backlot tour, especially the Roger Rabbit and Rocketeer set designs / vehicles. But it's nice to see the Rocketeer's jetpack on a shelf collecting dust in the new version of the backlot tour.
On a side note, recently returned from 3 days in Anaheim and had a great time at Disneyland Resort. It was nice to see stores / rides / things still in their places or returned to their former glory. World of Color is quite impressive but want to go back in 2 years after the upgrade at DCA is complete.