I know it's late to leave a review 1 year after launch, but here goes
((Spoilers ahead))
What did I think of this sequence? Well, in my opinion, not as good as the first game. Great art, I liked how the story was told, but my issue was with the characters. So, I think this ending just throws away any Koko development that was pre-established in the first game.
Yes, of course, you have access to an excerpt from Koko's diary in the first game and you see that she was a little crazy, but apparently she changes as a person. And she changed even more over the years. And in my point of view, it made no sense for her to do what she did in the end.
It was already apparently established in the first game that she would let you go or stay with her, so her suddenly acting like this now at the end of this sequence made absolutely no sense, and basically breaks everything that was already established in the character.
And with all that said, it doesn't make sense that after all that she imprision you after killing her own daughter.
As for Reiko's ending, it made a little sense, as she was a child going through a kind of "puberty" of her kind. She was uncertain and afraid, but with the right choices this should be avoided.
But still, the ending remains open, with a little or no closure.
Imo, it was not a good sequel. I understand the idea that Seiichi was just not in control of the situation, but it didn't work imo. Considering how good the first game was, I was disappointed with this sequel.
Again, it's all an opinion. I'm looking at everything from a critical point of view, it's not like it's just a "noooo i don't like bad endings!! Koko and Reiko should have a good ending!!!!" - I'm pointing out things that I saw as a problem in this sequel, and I hope that maybe one day there will be an update (even after 1 year) with a good ending that makes sense, because it is possible.