Like in Cyrodiil:
The Jemane Bothers line of quests were pretty good.
Where Spirits Have Lease was a good challenge my first time.
Through a Nightmare Darkly for the same reasons others have stated.
Lifting the Vale. Nice and lengthy exploring quest. Although I don't like the fact a person approaches you about it when you're not ready to do it (I guess I'm obsessed with keeping my journal tidy).
A Shadow Over Hackdirt. Intriguingly spooky town the first time through. Plus you get to rescue the damsel in distress.

The Order of Virtuous Blood. Nothing like some good vampire slaying.
No Stone Unturned. Some more good opportunity for exploring.
Ghosts of Vitharn. (SI) Help ghosts earn their rest.
Dislike:
The Wayward Knight. Farwil sure can be a
thorn in the side. At least you get a good reward for it.
Work Is Never Done (SI): A whole lotta tongs and caliper finding for only measly gold.