I never did understand why people loved Molten Core so much. Maybe it was the feel of 40 man raids, but for us people who played a decursing class back then, that's practically all I did the entire time for several fights. I mean god damn it.
Lucifron, Gehenas, Shazzrah, I think frickin' Harbinger ALL had those STUPID, STUPID curses. UGH. People like to bandwagon, but at least that shit didn't exist in DRAGON SOUL. Do you have ANY idea what it was like to decurse 40 people?
However, that's probably my second pick. I get the "atmosphere" thing for ToC, but those encounters were brilliant! Faction Champs is one of my favorite fights ever still!