I'm going to ignore all those answers and drop a complete curveball.

Brayflox's longstop from closed beta 2 if I remember correctly? It was the first proper dungeon test that I remember and dungeons played out in a radically different manner back then compared to how they are now.

The trend was to CC and if a BLM wasn't in the party, it was my job as WHM. Neatly lining up and managing mobs ready to be killed in a smooth and safe manner was highly satisfying and scratched an itch left over from my Everquest days. Brayflox having an abundance of wandering adds and several open areas rife for a butt pull made it even more dynamic and enjoyable too.

I'd absolutely love to see a dungeon like this again++

If that's not an acceptable answer, then it's Holminster Switch for me, it told a good story and visually it was rather unique reminding me of Westfall from WoW.