Fantasmic had really been built up for me by a friend who has an AP. I had some reservations because I had heard that some of the images and noises might be frightening for young children. For the first couple of minutes, I thought it was going to be boring (I just don't get the whole Fantasia thing), but it turned out to be, well, fantastic! My kids loved it, too.
Also, I actually found the waiting for the show to be pleasant. The weather was nice, we had a place to sit down, and we bought everyone lemon chills (because they take a long time to eat--something for the kids to do while waiting).