It's definitely one of my favorite expansions, maybe even my favorite. Mop had a great raiding scene at the time, Challenge Mode was introduced and those class armors are still some of the best visually satisfying sets to date.
Paragon buff for alt rep grinding, the Timeless Isle, Isle of Thunder, legendary cloak, the list goes on. People hated on the expansion because "lol kung-fu panda", which is still to me that silliest critique. It was a fine expansion and had so many great systems in place.