Long time WoW-er here.
My reflexes and ability to build muscle memory to the point where I can play multiple classes and specs well are still with me, but some of the game systems are needlessly complex (and sometimes irritatingly so).
For example, the whole flightstones thing is stupid. Why not have one currency class for upgrades (i.e. crests)? And why do we need 300 stones to make sparks?