I have watched this film 3 times and it has been able to play with my memories and throw me through a whirlwind of confusion every time I've watched it. Satoshi Kon is a genius in his ability to blur the boundaries between reality, dream and persona and this film is his finest example of this ability. This blurring experienced by the protagonist, Mima, is something the viewer is actively thrown into and experiences, entire scenes feel like fever dreams and will leave you paranoid on whether or not you can trust what is going on.
Despite its age, the themes touched by this film are still relevant today and it's able to hold itself together very well.
Definitely recommended going in watching this blind.