Played a few hours of Nightmare difficulty from the start of the game. I'm about six missions in I think and really the only noticeable spike in difficulty is the lack of items. Many corpses don't seem to have anything on them and only 1 in 10-12 boxes will have any supplies, which has made me very picky about crafting. Getting shot twice will put you down. Haven't been attacked by any androids yet. I'm actually getting pretty decent at sneaking. Didn't get killed at all in the medical area. Was actually able to trap a couple of droids in a small room, which was pretty funny.
One thing I have noticed is behaviors or scripted bits with the Alien that I've never seen before. Might just be that I never noticed them before. Examples are
Spoiler
when going too android storage the group just before the storage area gets attacked. The alien grabs one of the guys and takes him into the vent. A similar thing occurs again once a little later.
Doubt any of that has to do with the update.
The Alien behavior seems about the same. I haven't used any crafted items, weapons or flares on him yet though.
Gotta say the hud-less view is my favorite part.