I like empty rooms, especially if they have some sort of feature that would make a wandering monster encounter in that room more memorable (pillars, unstable bridge, fountain etc.) or a red herring feature that keeps players on edge. At the end of my last session, the party happened across the Bhaal Furnace in Stonehell and, having previously triggered a trapped crematory, spent a good amount of time figuring out how best to get through the room without triggering an unseen trap.