Agree with the above, class quests and exploration should be inextricably linked, dungeons should have an array of quests of their own. There still needs to be things to do "off the road" as it were. As mentioned, a Dynamic system like GW2 would help make the world immersive. Things like a Hunt/Mark system is also another way to feel immersed without feeling like you are completing quest 1 to 10 at hub1 before moving onto hub2.

I do think however that there need to be more substantial boss fights along the way from 1 to 50. The current boss type fights especially in the class quests and missions dont feel very epic or final fantasyish. Frankly there are no good boss fights until 50 and even then some of which are lacking. Granted it might backfire to make them too hard or to requiring a party every other quest, but some fights could be about endurance (seeing as most offline ff bosses are about endurance, mp or item management, rather than difficulty).