Yeah, I got the achievement there. (People who know what I'm talking about know what I mean.) It was quite funny because I was almost positive that it was an achievement, and there it was when I did it.
I'm about 4 hours in, or so. I started at Hard, thinking that it was similar to the difficulty on Bioshock 1. Wrong. It's a LOT harder. Closer to Insanity on ME2. I had to dial it back because having a slicer take a full bar on a regular basis was fucking with my enjoyment of the game. (Not to mention that the ammo it took to kill them was insane.) Even at Normal, the Adam extraction points are difficult.
I also noticed, at least from my first Little Sister, that there might actually be some consequences to saving every Little Sister. In Bioshock 1, if you saved every Sister, you would get enough gifts to offset the difference. However, I don't know if the same is true here, because (at least for now) I can't get to the Adam shop in Ryan Amusements to buy the upgrades over there.
Maybe I'll find that I can go back later on, and maybe the extra Adam will come later. Or maybe they "fixed" it so that you have to play good to get the good ending and play evil to get all of the upgrades.
Rosalina: But you didn't.
Robert: But I DON'T.
Rosalina: You sure that's right?
Robert: I was going to HAVE told you they'd come?
Rosalina: No.
Robert: The subjunctive?
Rosalina: That's not the subjunctive.
Robert: I don't think the syntax has been invented yet.
Rosalina: It would have had to have had been.
Robert: Had to have...had...been? That can't be right.