Vanilla: Exploring the new World, I didn't care about BiS items, how haste works, why I have bad talent tree. The new world was just something overwhelming and exciting that I didn't focus on my "raid team".
TBC: Going through the Portal to another world... I didn't know there will be another exciting thing in this game. Illidan, Kil'jaeden.
Wrath: Arthas... Wrathgate, going to Grizzly Hills(music + that atmosphere). Ulduar - TITANS!
Cata: A World Teared Apart + Deathwing(I wanted better boss fight, but still it's DEATHWING)
MoP: Nothing special, I didn't have "That Moment". I'm not a hater, I just can't find anything good for me. I'm close to "Asian Theme Stuff" everyday, and this expansion is just "blah" for me because it's pseudo-Asian thing, which is annoying me. The only thing that comes to my mind is Lei Shen, he was epic.