I strongly recommend playing this if you already bought the game at launch. It won't cost you anything, and the game is awesome.
World bosses are actually hard now, we fought 30mins against that lamia thing in Abah's Landing. It killed me at least ten times, mostly oneshotting me. It was so great when we managed to kill it finally! There was about a dozen guys battling it.
Dungeons are harder to solo too, at least for me...
I really like the quests in this game, and there's no doubt that they'll make a great Morrowindy DLC for this. So many things done right lately.