I appreciate you actually explaining in detail why you didn't find the last episode very good. I personally thought it was alright storywise but I only saw comments saying that it sucked without really saying how or why they thought so.
Personally, I mostly say that the ending sex scenes what really makes it a little disappointing for me. Like I mentioned, storywise, I think it settles what needed to be settled. Maybe anti-climatic for some but I do have some thoughts on that actually.
Though yeah. I think the story as a whole is pretty basic (like the story beats seemed obvious to me) to be honest and some people over thought some parts of it which made them expect more from a conclusion. It's well put together but nothing too mind-blowing. I feel more like characterization is where this game shines and for me, every character fulfilled their role and didn't over stay more then they needed to. So yeah, for me decent ending. More then I can say for a lot of games in this genre.