Here's my review of the stress test.
My gripes:
I was honestly a bit disappointed with the battle art. I was anticipating something more akin to the trick weapon transformation from Bloodborne that completely changes how the weapon is used in interesting and useful ways, but the implementation basically just grants an additional moves that I didn't find myself using very much. The most useful one, imho, was that of the wandering knight's short sword - very useful for guard breaking and stunning. I feel like it's only a slightly more interesting version of power stancing from DS2.
I only liked two of the weapons - the short sword and the spear. The others felt underwhelming, especially the claymore. It desperately needed more dps or more stun locking; two swings barely did anymore damage than two of the short sword and completely drained stamina, making a retreat impossible as the stun lock was too short to recover enough to roll out. I never really understood the gripe about Bloodborne's lack of weapons, as I felt that the Souls' games overabundance and clear hierarchy of weapons just made most of them obsolete. It looks like DS3 might head in the same direction as the rest of the Souls' games?
I have mixed feelings about the Dancer boss. It looked at first like it was going to be just every other boss from DS2 - big dude in armor. Its movement, however, was very interesting. I actually liked standing back to just watch it move. VERY enjoyable boss fight. However, mechanically, it again felt like every DS2 boss: get behind it, hit it twice, back away from AoE. Beat it on the first go, healing only once. I'm hoping the DS2 strategy won't work for every additional boss.
Now, for pleasant surprises:
Charged R2 attacks, straight out of Bloodborne! Absolutely delightful. And, unlike in Bloodborne, it felt worthwhile charging up for something other than a backstab or PvP bait. Perhaps it has to do with the slightly slower relative pacing of DS3?
I also did't try it with other weapons, but I found directional input and proper release timing of R2 for the Northern Warrior's axe prompted it to do different things (e.g. overhead smash vs charging uppercut akin to Gascoigne's). This was what I was looking for in battle art, so I'm happy to see some implementation of it. Will test with other weapons tomorrow.
Backstab! Yay! Kicking! Yay! Praise the sun!
OP covered a lot of it, but I want to add some speculation. It seems the denizens of the outskirts of the castle here are worshiping the center in some way. I'm guessing it houses the current Lord of Cinder.
Some undeads seem to have 'ascended' in some way, their legs having turned into the trunk of a tree rooted in the ground, and their arms outstretched to the central castle.
There is one undead who sprouts a weird snake-esque variant of what really looks like Manus' arm to me. Something abyss-like drips from the Dancer in the cutscene at the start of the fight. I'm guessing the overarching plot has something to do with the encroaching abyss and its effects on the former Lords of Cinder.
Looks very promising. As /u/SaveVsFail said, it looks like a game 6 months from release, but it looks like it has all the making for the greatness of DS1. :-D