Cleric stance and the general juggling involved in balancing healing and dpsing with a side dish of MP and enmity management.
I even miss those "shit shit shit got locked in cleric and my tank is getting torn to shreds oh fuck" moments. I enjoyed the risks many things typical for ARR involved.
The teeny bit of costumization via stats and cross class skills. Finally getting every cross class skill I needed was definitely an achievement for me and felt great. Doing dungeons in unsual comps when no tank was available but you really wanted to get on with the story. Titan Egi, you were the real MVP.
Watching Dragoons use Blood for Blood or Black Mages Convert at a really, really bad time and hovering over Swiftcast because everyone knew how this would end.