On the very first day that SQ flew it to LHR, I happened to be on my way to Spain for an exchange rotation in Madrid and I was connecting via LHR. I knew SQ was flying it to LHR that day but I figured that it would be unlikely that I'd get to see it.
...and then we taxied right behind it while it was sitting at the gate. It would be another 7 years until I would manage to get aboard one (a trip that involved my first A340 and my first A380, thereby taking me on both Airbus quads for the first time in my life in the same trip).
I have only ever flown on two, one on AF and one on LH. It's a quiet aircraft, but I find that the thick sidewalls make it difficult to see out the window, and the sheer size of the thing makes embarcation and disembarcation take a long time. That said, that size also makes it a very gentle ride. You barely feel any acceleration at any phase of flight. For me, I dislike that. It makes me feel disconnected from the experience of flight. That may be popular for most passengers, but for me, I prefer the sights, sounds, and feelings of flying.
I understand precisely what you mean. My first A380 flight was a QF to SYD from LHR. I remember sitting upstairs wondering when we were going to take off, then suddenly realising we were already rotating! I know that sounds unlikely but it is true: it was so quiet, I didn't even hear the engines roar as the aircraft did its takeoff roll.
I really enjoy the upstairs solo 'coffin' seat on BA on the overnight SFO to LHR, which is a regular for me. Very private, very smooth, very quiet. I get onboard, recline into my own little cocoon, and I am undisturbed until about an hour out of Heathrow.
On the other hand... as you note, boarding an A380 can be quite chaotic. Have you ever witnessed the end of the A gates on the international terminal (Gates A13-15) at SFO when an A380 is awaiting boarding? It is chaos. Boarding an A380 in SIN is not fun, if they delay the boarding for whatever reason - remembering there is gate security at SIN, so once you are in the gate, you are incarcerated. And those gates can be cramped when it's a full flight.
Another negative is that the aircraft is so quiet, it makes other noises more noticeable. For example, passengers can hear crew talking in the galley. This can be disruptive on a night flight.
I sound like I am complaining, and I do not mean that. I really enjoy the A380 very much, and always look forward to flying on one. I nearly always take the later A380 flight from SFO instead of the earlier 777 flight. I just wish it was prettier to look at.