I'd say yes and no. To me, the one and only defining characteristic of horror fiction is that there is some sort of fear at the core of it. But there are different kinds of fear, and they can be closely tied to a lot of other emotions. So there's absolutely room for a horror to highlight emotions like nostalgia or betrayal. But if it's a horror story, to me, there must be some kind of fear associated with that emotion. If we're talking about nostalgia, it could even be something like fear of losing hold of the past. That could still be a horror story. But if it's *just* about nostalgia, and fear is completely absent, then I wouldn't think of it as a horror novel even if set in a "horroresque" environment. That said, it could still be a very good story, and it might even still be shelved with horror. After all, genres are more about marketing than anything else, I reckon. A good story is a good story regardless of what section it's in.