I've been playing this game a lot over the past month or so. I'm not really sure if there's an end goal, or a way to get every key item, or how many NPCs you can interact with using the key items. But, I just feel good spending time in the world. Something about the melancholy atmosphere is just really calming and relaxing to me, especially during periods where I feel depressed.
I say all of this to basically say, I think you've made something really special. If this was all the game was, I think I'd be happy with it. Being happy with it feels good. But, if there ends up being more, I'd be happy with that too. I think that shows that no matter what, this is something really cool and interesting to think about.