This opinion will have spoilers and I am going to divide it into 3 points, the animation, the plot and the message.
First speaking of the audiovisual, it is crazy, all the details are very careful, it has incredible fluidity, backgrounds to match and what would stand out the most is the color palette and the good use they gave it to emphasize and elevate many moments , they knew how to convey the despair of the world very well and they also knew how to highlight the small happy moments that the characters can have. As for the music, it is well implemented and thanks to it it accompanies different emotional moments very well.
Regarding the plot, it could be said that it is similar in several ways to Alice in Wonderland, but this time the point of view we have is that of someone inside the place and not that of the person who is lost. The narrative of the film seemed abstract to me, they leave us some clues in a tenuous way and this may mean that not many people understand everything 100% when watching it for the first time, but I do think that the message is clear.
I personally liked the message, it is an optimistic message since what the author wants to tell us is that although we do not have a future, objective or a clear goal, we should try to continue improving, getting excited, having fun in the same way, the example is like Masamune He considers this and decides to look for variants within the static life he was leading, an example could be the relationship he establishes with Mutsumi, improving as an illustrator even though he did not have a clear goal or having fun with his friends despite everything, we can also see How there are people who take advantage of circumstances like this to gain status despite everything. Another thing that I liked is the temporal reference to what is called in Japan as “The Lost Decade” since the film is initially set in 1991 and there is a very interesting dialogue from Masamune's grandfather in which he emphasizes that what This reality is not a punishment, but rather the gods encapsulated the happiest moment of the town before it ends.
It is an optimistic message about the search for identity, the growth and expansion that we can have as people and never losing the feeling of being alive.
A contrast that I liked was how those who were trapped wanted to escape from the reality they were living in order to find their reason for loving life and how the visitor found what he loved within this place and wanted to stay.