After playing this game for the last year incessantly I have definitely encountered quests that I return to again and again, and others that fell by the wayside. I was wondering what the larger community thought as well too see what, if any consensus there is? Nightmare mode is a different story because they have really reinvigorated some crappy quests.
Mind you I have not played the Battle of Lake Town or Stones of Erech.
Best Quests:
Journey Down the Anduin, for sheer excitement when you finally beat it. Also it is a solid quest that I play when I am just looking to test some decks.
Conflict At the Carrodck, is pure gold. Fighting 4 trolls at once is just too much fun. All around tough quest.
Siege of Cair Andros, this quest can be really difficult for some, but I love the decision making involved in the quest. Trying to save all 3 locations or only going for a specific 1 can really change the quest a lot. And I love the siege mechanic.
A Knife in the Dark, all time favorite
The Three Trials, This one only recently came out but it is already one of my favorites. All around fun, and the endless combos are great for variability.
Worst Quests (Excluding Nightmare):
Hills of Emyn Muil, all around dull
The Dead Marshes
Into the Pit, especially in single player this quest is just location after location with some tiny enemies popping up every so often.
The Long Dark
Peril in Peralinger not a bad quest, just for me endlessley frustrating, so I tend to avoid it.