Another problem is that the class quests (that are mostly very nice and involved story-wide) are, by definition, distributed between classes. There's unfortunately, a lot of high quality quest-related content with lovely cutscenes and characters that many people simply don't experience, because they don't play all classes to level 36.

Just as I suggested above with the main storyline, I would condense the level progression and add a longer/more epic tail to the class quests as well, as proposed in this thread.