I like the writing and the visuals and much of the setup, but I have to admit there's one aspect that didn't work for me at all. <Spoilers follow, of course.>
The endings--I went through it twice, once letting her go, once killing her--make it clear, when the protagonist is on the phone to their mother, that they're fully aware of what the woman in the basement is, why she's dangerous, what kind of threat she poses. Before that, though: I think it can be very interesting to play "what the character knows" against "what the player knows", but the protagonist seems to make it clear that they don't know who she is. "There's no way my grandfather kidnapped some woman"; at one point they literally say to her, "What are you?". And that didn't work for me at all. If the character doesn't want to tell the player everything they know, that's fine, but ultimately the protagonist seems to know exactly what she is, and having them act in ways that suggest they literally don't know--until the end--felt like a bait and switch to me.