From what I've experienced, the quest for this DLC is just too skeletal. No conversations about the Overseers past, explaining to her what the world is like outside, just right to work. So far I've only managed to clear out all of the tunnels and caves, and sweet lord did that just go on and on. Clearing a wall of rubble, to only then quickly switch to combat is clunky as all hell. I feel like this could have been done better by having you plant C4, moving back, blowing it up and then heading in, without ever having to go into Settlement Mode. I do like the share size of the place, that we're given enough room for a couple of Vaults, yet the janky nature of building killed it for me. Too many times did I find myself saying, "Fit, you fucker!" Or to start building rooms a certain way, only to then discover I couldn't make it work and had to undo parts of it, or that I needed to place support structures if I wanted higher floors. Frustrating.
It's all very mixed for me, but I will point out a few good things: The Vault comes with a massive water plant that produces 100 water, there's two new buildable reactors for power, and the entire settlement's huge and competes with Spectale Island for share building room. That's about it, though.
I haven't gotten far enough to preform experiments or to see what the rewards are like.
Edit: Corrected the amount of water produced from the plant.
