-Axe the filler. There are many options to reduce the quest load without sacrificing world building or characterization:
*Removal of fetch quests
*Removal of investigation "dead ends"
*Quest-specific fast travel (e.g. "...bla bla now let me teleport you to your next locale!")
*Consolidating quest steps. Instead of "Travel to B, kill 3 guys, return to A, travel to C, kill 5 guys, return to A" we could have more A->B->C->A quests.
-Frontload more skills. Give every DPS class an AoE by 15. Give every tank a threat stance by 15. Give everyone some oGCDs by 30. Etc. Nothing makes you want to drop out more than spamming two DoTs and a weak nuke on every. single. mob.