Maybe not a life changing experience, but seeing the Monorail when you first hit the property. I was just telling my wife the other day this same thing, since we are less than a month away from going to the World.
Upon getting closer to Disney, since we are driving, when you first see the Disney World signs that are in the state sign color of green the excitement starts to build. The excitement is even more when you finally see the purple Disney signs that are on property and the big Walt Disney World sign. My 'WOW' moment or tear jerker moment is when I see the Monorail beam for the first time and again when you see the Monorail cruising along on that beam. That is when it's all over and can't wait to get into the house of the mouse and leave reality behind and enjoy another amazing Disney vacation. Nothing else like it.