1: This mission contains easily the best use of the Soul enemies I've seen. Putting them in a Deconstruction Zone style level is a good way of keeping the tension from dropping too low due to clearing the area of enemies.
2: I have to say I don't agree with practically requiring the player to use a gun to get past the very first corridor. I tried going in with just a Divine Avenger and a Shivermist Buster, and, well, that didn't go well! I used the sword's charge attack to hit the Sparkies, but that was very difficult to do while dodging the Souls and bullets, and I ended up dying before getting to the open area. Very relatedly, there's some sort of bug involving the throwable pot in that spot: It shatters if thrown straight ahead from where it appears. I suggest fixing that bug and moving the Sparkies farther apart so they aren't blocking the switch from being hit by the pot.
3: There's a bug I encountered on the first floor where the only key had been placed in a locked area, preventing me from getting to it.
4: The design of the boss was cool, but the fight took ages and was honestly pretty boring. I was using a Divine Avenger and had to spend a long time hitting and dodging the tendrils between each opportunity to actually deal damage. Dodging and landing a hit or two was easy, but took so long I ended up playing recklessly and getting hit due to impatience with the monotony. Patience is not something good game design tests.
So what can be done about the boss? Well, if it's true that damaging the tendrils enough is what makes the boss become vulnerable, then I'd say the amount of damage that is "enough" should be reduced. But that will make the fight even easier! So then I'd suggest adding more to the fight to make it a challenge. One possibility is to make the lasers move slowly while active, requiring players to think on their feet a bit more. Also, Spookydemi suggested adding Phantoms, which I think would be a great addition to the fight. Shock-themed Phantoms that don't stay "dead" for as long as regular Phantoms would be preferable, and I'm sure it'd be easy for you to make some. Them being Shock-themed would be appropriate, especially since you're adding a bunch of other newly-Shock-themed enemies in this mission. Heck, if they can inflict both Shock and Curse, that'd further encourage the player to use a Divine set for the mission. (Using a Divine set isn't currently as big of a help for this mission as using a Dragon Scale set is for Compound 42, but I still had the thought that you had it in mind a bit here.) As for the amount of time they stay "dead"... basically, a balance would have to be struck between rewarding the player with a reprieve for killing them and not making them stay dead for so long the fight becomes too easy.
1: There is definitely a bug around the pot on the other side of where the two Sparkies spawn in the first area. It's a small barrier in the middle of the pot generator that the player can't pass through and therefore the pot can't be thrown through. Please fix this so that the pot can be used. Or just remove the pot altogether if you're going to force the player to use a gun in the first area, since that's still the case, due to the fact that it would be impossible to throw a pot in between the Sparkies even without the glitch. (Of course I don't recommend that. Altering the layout so the pot can be used to break the barriers and hit the switch would be very preferable.)
2: I know I said in my first post that adding Soul enemies to a Deconstruction Zone type area was a great idea, and I still think that's the case. However, the first floor still gets dull once the other enemies are all gone. Now, this may have just been my experience due to soloing the level; perhaps it's more interesting in a team, due to different players being able to search different areas and work together to bring back totems. That being said, I'd like to see more traps on the first floor, so that navigating the level doesn't become quite so trivial once the enemies are gone. I know I'm not the only one suggesting this. Actually, it would benefit the combat too. The complete absence of Kats in this mission makes sense story-wise, but leads to pretty easy fighting in the main part of the first floor due to the large area to work with. Adding more traps would put a little more restriction on the players' movement, making the Volt Knights in particular more dangerous.
3: The messages on the second floor were far better as two pages than one, IMO. Them being on one page, plus the addition of "First message:" and "Second message:", changes the feel of the messages somehow. I found it much more captivating to go up to a shiny thing and be shown the message "help us", only to click "Read more" and have it change to "THE SITUATION HAS BEEN RESOLVED PLEASE EXIT THE FACILITY" (if I'm remembering the line right).
4: The boss was definitely improved. And now I know that I don't have to attack the tendrils to make the boss become vulnerable. Though, because of this, the boss ended up being able to be cheesed somewhat by holding down the shield button and wandering around. In a party of one, the fight ended up still being slightly tedious due to this. One possible way to combat this would be to make the enemies spawn continuously at intervals, rather than the generators waiting for last enemy they spawned to be killed before they warmed up to spawn another. That way the players would have to fight the constructs to beat the boss. I don't know how good of an idea that would be if the number of tendrils that appear increases with party size. But if that number is always the same, the fight needs something like my idea here, IMO. It needs more fighting!