The art is very beautiful and the environment is visually enjoyable to watch, I really loved the colors and the graphics. The story itself had a lot of potential, especially when it comes to the mystery character.
However, the story just doesn't go deep enough in my opinion, and has the focus on the wrong thing. Instead of exploring the real mystery about the situation, the whole focus story wise is on the two main characters and how they are "like siblings", except they are just not that interesting. These two don't develop at all, they stay exactly the same and you can predict exactly what they will do. They keep repeating the exact same story about their life by thinking about memories that keep repeating pretty much the same point, as barely anything really happened in their life to begin with. They keep arguing about the same childish things in the most unrealistic times, when there are clearly more important things for them to worry about. Everything about these two characters is just very repetitive through the whole movie, even though everything else about the movie could be way more interesting, and gets completely neglected by the script. Majority of the other characters are just there for the sake of saying there are more characters, and we barely learn anything at all about them.
There are so many great directions this could have gone if the story was actually about the drifting house and if they explored Noppo's backstory more, but sadly it ended up mostly as a drama story about two children who keep talking about how they use to live together, and argue for no reason in every situation that makes zero sense to argue on.
All that said, everything other than the story about these two characters is still nice to watch, it's just hard not to feel like there are so many easy ways that this movie could have been better.