I travelled on the A380 earlier this year JNB-CDG with Air France. The main difference is the noise, definitely compared to the 777 KLM flew me down there on. I was surprised at how quiet it was. I was behind the engines on the upper deck and I could barely hear them. Someone else did mention the gap between the window and the little bit you see through from the seats. I also found it a little awkward to see directly downward, unlike single decker planes, however it's not a disadvantage as such, just takes getting used to it you're more accustomed to other planes. I did like the little cupboard type pocket that AF had next to the upper deck seats (in addition to the seat back pocket), not sure if it is standard for the A380, but it saved getting up to use the overhead bins.
The actual flight and ground manoeuvring were so smooth I didn't notice we had started to taxi at JNB until the safety came on, by that time we had been pushed back and were on our way to the runway, but I felt nothing!
Have a good trip!