Having just passed the 30, for me there's still quite a difference
The best way to play, other players are NPC's with an advanced AI and can sometimes become henchmen for difficult quests
Also, I think the problem from Cyrodill was the fact that enemies were too high level to put in the 20-29 soul gems, and the mobs in the PVE areas too low. So after level 20 issues with getting the correct filled soul gems for resses.