Pretty good game, loved the twist at the end, these are my thoughts on it.
I do have a few questions though, what happened to the uncle, and what happened to us after we open it? Do we just send the box to a new person?
The idea was that the creature trapped inside the box eats away at your sanity and tries to compel you to open the box and release it. I didn't really explain it, but I think my idea was that the uncle was trying to mail the box somewhere safe, but the creature tricked him into sending it to his nephew instead.
As for what happens after opening the box, the creature escapes and fully takes over the nephews mind. I had intended to make a more fleshed out sequel where you play as the uncle who returns to construct a new box and trap the creature again, but I got a new job shortly after making this and haven't had nearly as much downtime. Maybe it will happen someday.