I don't know if this idea already surfaced here. If it has, I'm sorry if I'm duplicating it.
I love Descent - 2nd Edition.
I would love to see a big expansion that deals with city adventures (roads, houses, bars, blacksmiths, inns, city bandits, robbers, city mitilia, etc.) and sewers beneath the city (giant rats, wererats, sewer monsters in general).
I think that it would give a new dimension to Descent and create the potencial for new and different adventures.