One of my personal highlights was the Disney Archives exhibit. A few years ago we visited the Ronald Regan Library for the Disney Archives exhibit which I loved and this years exhibit at D23 was just as wonderful and great. Loads of great memorabilia, costumes, attraction vehicles, and animatronics!
The Matterhorn Abominable Snowman (named Harold) was recently retired in the attraction and he visited the expo! He's amazing up close and personal, which was nice instead of trying to get a good look at him from a fast moving bobsled while screaming my head off. Other highlights include the first Disneyland ticket, Walt's name badge, a reading and original copy of Little Man of Disneyland by John Lasseter, the Alice animatronic, Country Bear Jamboree pieces, a wonderful Club 33 set up that is pre-referbishment as well as Fantasmic! costumes and parade pieces.
This exhibit was well worth the wait and taking the time to move though and really enjoy the presentation. I'm so happy this was there.