Mt. Hyjal was strongly hated by people who were progression raiding during TBC. I can't think of a single person I knew in my guild or in the other raiding guilds on my server who enjoyed that raid instance. Mind-numbing waves of trash that you had to repeat if you wiped followed by push-over bosses. The only boss who was not a total push-over was Archimonde and that fight was just a clusterfuck of people whining about the Tear not activating when they pressed it.
The nostalgia's gotta be pretty strong if anyone's pointing to Mt. Hyjal as an example of a good raid.