People were freaking out a bit at first about Ruins of Ampador. The dungoun itself is a good example of fun mechanics, though.

DPS the gormund's belly to quickly break your friend out.
Tank co-ordinating with DPS to recieve the highest stacks of the debuff (We actually had a DPS take a debuff at one point, and he had to off-tank while we quickly nuked another one)
Coordination of Doors, smart positioning of bursting AoE's on Diabolos. As dragoon, I often can solo-handle this, but I imagine it would be a lot harder for a party that's not very... smart, about how they handle it.

Fun mechanics like this, that aren't mindless like FATE grind's 1-2-3 gameplay, are what I love to see.