I finally had some decent drops including a rather good unique after many attempts so it was purely bad rng.I've had several uniques drop from them, including one this evening that enhances my ice sorc build significantly ( frozen enemies that die have a 15% chance to trigger frost nova ). I've found the higher tier nightmare dungeons appear to drop a better quality & quantity of loot. But as usual, there is RNG ... so sometimes it doesn't work out, and on another run I end up with a dozen legendaries. It can get a bit wearing running Nightmare ( or Ancestral ) dungeons constantly, but I break it up by doing helltide events, grinding reknown points and doing mini events for Tree of Whispers caches. Only thing I've not dabbled with is PvP but I've scouted out the zone fully.
I'm also finding having a plan for how I want to fill out my paragon boards is keeping me motivated for running nightmare dungeons. Getting those glyphs to lvl 15+ so they have an influence radius of 3 can really boost your character's power.
I'm still not big on the dungeons though. Sick of picking up 2 objects and carrying them back to open a door. Definitely need to break them up with other activities or I'd have given up by now.