In terms of class based fights, I remember Gladiator 15 when ARR first came out. We had other classes unlocked at 15 back then, not 10 and it was do or die. The forums were full of threads screaming about this quest and I'm pretty sure it helped set the stage for avoiding Tank as a class. Keeping the paper thin healer alive, tanking multiple targets and somehow dps'ing them with no skill bar. It's likely the one I repeated the most.