In Pilgrim's Peril the shielder doesn't protect the healer or the rezzer. That may be intentional, but obviously the quest would be more difficult if you had to take down the shielder and then get the rezzer before the shielder could be raised and re-establish the shield. Lever for final boss moved to an easier to spot location.
In Stolen Power if you fall in to the 'water' in the first room there doesn't seem to be any way to get back out. However, tougher characters on lower difficulties have time to recall out and re-enter. Unclear if that is intentional. The titan now stops attacking if you kill the illithid - which is a nice change.
In Horde, I made a stealth character this time, but wasn't able to sneak past the giants. Is definitely going to take some practice, especially if attempting to get the optional side chest. That dropped a single card for me... not sure if that was spectacularly bad luck or the optional chests just have a lower drop rate for cards than the end chests.
In Astral Ambush the levers have been changed to gravity switches, but the messages haven't all caught up;
"The lever activates, and one of the signal crystals by the barrier flares alight."
"With both levers pulled, the fortress's barrier collapses in upon itself, revealing the passage beyond."
It is possible to overlook the green and/or blue switches and still get past the barrier they control. This results in being able to 'finish' the quest with the 'enter the fortress' objective incomplete and thus not receiving XP.
I don't remember the protective bubbles on the illithids and death slaadi in the last preview, but I had a melee build so I might have missed them. From what I can tell they are strictly a range shield... like a smaller version of the Balor's fire circle in Fire Over Morgrave. So you can still take them down with ranged or spell damage... you just have to be in melee RANGE to do it. Very nice. Could have some good synergies with group tactics like in Pilgrim's Peril (e.g. melee range shield on a healer that you have to jump across several pillars or get past a wall of melee troops to reach). Also pairs well with mobs that do aura / close AoE damage.
From what I've seen so far it seems like 0, 1, or 4 of each type of card drop on Casual difficulty and 0, 1, 4, 8, or 12 on all other difficulties. Not enough data to be sure, but it also seems like those skew towards the lower end (i.e. 0 and 1 are more common than 8 or 12).